Impact of waterlogging stress on grafted avocado (Persea americana) seedlings growth and physiological performance

Abstract

Agricultural fields prone to waterlogging condition induce physiological stress on fruit trees as it affects root respiration and nutrient uptake. However, the information on the growth performance of avocado under waterlogging condition is limited, particularly in terms of morphological and physiological performances. Therefore, this study was designed to evaluate the performance of avocado rootstocks under different waterlogging levels under shade condition. The experiment was conducted using a complete randomized design with factorial arrangement using Ettinger variety as scion that was grafted on Guatemalan and Mexican rootstock races at three waterlogging levels (50%, 75% and 100%) in three replications. The result showed that morphological growth of avocado grafted on Guatemalan race outscored in number of buds, shoot growth, rootstock elongation and scion shoot tip growth compared to the one grafted on Mexican race. Similarly, photosynthesis, transpiration and stomata conductance were significantly affected by the races, waterlogging levels and interaction of the two main factors. The result indicated that the Guatemalan race significantly improved photosynthesis, transpiration, stomata conductance and water use efficiency nearly by 50% in all waterlogging levels as compared to the one grafted on Mexican race. However, the smallest transpiration and water use efficiency were recorded at 100% waterlogging level from the Mexican race. Generally, the study revealed that Guatemalan race used as rootstock gave a strong morpho-physiological performance as compared to the Mexican race. Similarly, waterlogging level at 75% induced strong morphological and physiological performances in Guatemalan race compared to the seedling subjected to 50% and 100% waterlogging. Thus, the finding revealed that the Guatemalan race can be a potential rootstock under waterlogging/saturated soil condition in loamy sand soil texture.

Keywords:

• avocado rootstock
• waterlogging
• respiration
• stomata conductance

Public Interest Statement

This article provides information on waterlogging, which is an important environmental stress that causes a significant impact on the overall growth and development of fruit crops. The study specifically investigated the effects of waterlogging condition on the growth and development of grafted avocado seedlings. The finding also confirmed that different avocado rootstocks responded differently to different waterlogging conditions. Therefore, it is concluded that avocado rootstock negatively responded to excess soil moisture unless tolerant rootstock is carefully selected and optimum irrigation level is determined based on the sensitivity of rootstocks. In addition, a considerable attention should be given to the soil texture as it determines water-holding capacity and thereby irrigation frequency.

1. Introduction

Avocado is among the most economically important subtropical fruit crop that belongs to Lauraceae family. In Ethiopia, despite the presence of suitable agro-ecological conditions and economic value of the crop, the production and quality of avocado fruit produced are below the export standard. This is mainly due to the lack of suitable scion and rootstock cultivars that adapt to various biotic and abiotic stress conditions. The lack of appropriate agronomic management for the crop is another challenge to have a sustainable avocado production in the country. As many varieties of avocado trees are susceptible to moisture stress, salinity and root rot disease, it is important to identify and select a specific rootstock variety that performs well under biotic and abiotic stress conditions. Selecting the right rootstock has become an important factor as it is evident that rootstocks have a potential to tolerate the soil condition and influence the performance of scion as well as the fruit quality and productivity of the tree plant. Moreover, improved rootstock for commercial production is also used to induce alternative bearing for sustainable productivity, regulate vegetative growth and regulate tree height. Although, plants are sessile by nature and exposed to different environmental stress conditions, they have their own mechanism to cope up with the various stresses including stress induced by the current changing climate condition. Even, on a single plant, the root system and the shoot system both exist in very different environments, and each with their own set of environmental challenges. Hence, selection of scion varieties (shoot part) and rootstock varieties (root part) to fit to some of these challenges is significantly important to improve the productivity and quality of fruit yield. Arpaia et al. (1992) reported that a long-term approach towards increased avocado tree productivity could be achieved through a plant breeding program designed to identify both improved rootstock and scion selections. Historically, rootstock was developed in the early 1970s from seedling of avocado species to avoid the damage caused by root rot disease (Mickelbart et al., 2007). However, due to the possibility of an increase in moisture stress due to climate change and under limited irrigation facility and excess moisture level, the search for more drought-resistant and waterlogging rootstock has been an interesting goal for fruit crops (Serra et al., 2013). Drought, waterlogging and salinity have a broad range of effects on plants growth performance, and therefore there are also many different mechanisms for plants to tolerate these stresses.

Currently, due to climate change, most of the fruit farms are prone to periodic flooding either due to poor soil properties and rising water table from time to time. Additionally, the water table has been artificially raised in the area were irrigation of fruit trees is commonly practiced and improper irrigation frequency is taking place. These activities have resulted in a recent increase in the severity, duration and extent of flooding in avocado fruit production areas that were previously subject to only rare and minor flooding during the rainy season. Flooding detrimentally affects many tropical and subtropical fruit tree species including avocado trees (Schaffer et al., 1992). The primary effect of flooding on avocado crop is a reduction in root and shoot growth due to depletion of soil oxygen (Schaffer & Ploetz, 1989). Lack of soil oxygen is often referred to as hypoxia or anoxia. Hypoxia refers to the reduction of oxygen below optimal levels and occurs in poorly drained soils or during periods of short-term flooding. Anoxia refers to a complete lack of oxygen that generally occurs in soils after a period of prolonged flooding. Flooding reduces the transpiration rate of avocado trees (Ploetz & Schaffer, 1987; Schaffer et al., 1992) and this most likely results in reduced stomata conductance rather than a hydraulic effect, since flooding did not significantly decrease the xylem water potential (Schaffer et al., 1992). Flooding also alters the oxidation reduction status of the soil, reducing the redox potential due to chemical changes and various by-products of soil microbes (Ponnamperuma, 1984).

In fruit trees, the length of survival in flooded environment is dependent on the species and sometimes the cultivar. A previous report indicated that, for grafted trees, such as avocado, flooding sensitivity is primarily due to the rootstock and not the scion (Schaffer et al., 1992). However, little information is available regarding the performance of both clonal and seedling rootstocks of avocado in waterlogged conditions. Therefore, the current finding was intended to evaluate the morpho-physiological performance of avocado races rootstocks at different waterlogging levels.

2. Materials and methods

2.1. Description of study area

The research was conducted at southern parts of Ethiopia Sidama Region, Dara district, at Tefere kela nursery site under shade condition. The nursery site is at about 350 km from Addis Ababa, and 17 km from Dilla University. It is located at 1,850 m.a.s.l altitude and 6°30′0″N, 38°24′0″E longitude and latitude, respectively. The area receives an average rainfall of 1,700 mm per annum, with an annual mean temperature of 27°C.

2.2. Environmental condign of experimental area

2.2.1. Temperature and relative humidity

The maximum and minimum air temperatures of the experimental site (during the experimental period) were 32.4℃ and 11.7℃, respectively. The maximum relative humidity in the shade house on daily basis (99.00%) was recorded at 2:12 am (night before dawn) which coincided with shade house minimum temperature (17.3℃) and minimum vapor pressure difference (VPD) (0.31) (Table 1). Likewise, shade house daily minimum relative humidity (56.4%) was recorded at 11:12 pm which coincided with maximum daily temperature (27.3℃) and maximum daily vapor pressure deficit (1.58). Table 1 indicates that the relative humidity during daytime (in the morning session) induced higher transpiration of the leaf due to higher VPD.

Table.1. Average temperature (°C) and RH (%) recorded for 24 h for 1 month in the shade house during the experimental period (from 15 May to 14 June 2020)

Time	Temp (°C)	RH %	VPD	Time	Temp (°C)	RH %	VPD
12:12:00	27.3	58.8	1.45	00:12:00	18.4	82.2	0.38
13:12:00	23.2	69.2	0.88	01:12:00	17.9	82.6	0.36
14:12:00	22.9	71.9	0.78	02:12:00	17.3	84.2	0.31
15:12:00	22.1	74.6	0.68	03:12:00	17.6	84.1	0.32
16:12:00	21.9	78.8	0.56	04:12:00	19.4	82.3	0.40
17:12:00	21.4	80.4	0.50	05:12:00	21.3	76.8	0.59
18:12:00	21.5	81.3	0.48	06:12:00	23.1	71.9	0.79
19:12:00	21.2	81.1	0.48	07:12:00	24.5	66.2	1.04
20:12:00	20.7	80.4	0.48	08:12:00	26.1	62.1	1.28
21:12:00	20.2	80.1	0.47	09:12:00	26.0	63.4	1.23
22:12:00	19.5	80.6	0.44	10:12:00	27.5	58.3	1.53
23:12:00	18.9	81.5	0.40	11:12:00	27.3	56.4	1.58
				12:12:00	27.3	56.4	1.58

2.3. Experimental materials and treatments

For this experiment, two avocado races (Mexican and Guatemalan) were used as rootstocks which were grafted with the scion material collected from Ettinger avocado cultivar (popular avocado cultivar in the last 60 years in the study area). Waterlogging treatments were applied throughout the experimental period based on the field capacity estimated using a pressure plate apparatus (Pradhan, 2015), where 50%, 75% and 100% waterlogging levels were achieved at four, two and everyday watering intervals, respectively.

2.4. Experimental design

The experiment was carried out using a complete randomized design in factorial arrangement using two avocado races (Mexican and Guatemalan) and three waterlogging levels (100%, 75% and 50%) in three replications. The 100%, 75% and 50% waterlogging levels were developed by irrigating the experimental pot at one, two and four watering intervals, respectively, with predetermined water in litters through the experimental period.

Each experimental unit consists of four pots per plots. Each pot was filled with 3:2:1 ratio of top soil, compost and sand, respectively, forming 2 kg of composite soil media. The prepared avocado seedling rootstocks were planted in pot filled with soil, and the actual waterlogging treatments were applied after successive grafting was achieved and the graft union was well established (at 45 days after grafting).

2.5. Experimental procedure

Matured, healthy-looking and vigorous avocado seeds were collected from Mexican and Guatemalan races, and their seedlings were raised to use as rootstock. The seedling took about 121 days to reach the pencil size and be ready for grafting (Figure 1). The grafting was made at 15 cm height of the rootstock with the same size of scion (Ettinger avocado cultivar) having three to four buds.

Figure 1. Seedling avocado rootstocks ready for grafting.

2.5.1. Scion selection and grafting operation

Vigorous, healthy-looking, young shoots of 12–15-cm-long uniform pencil-sized Ettinger avocado cutting with three to four buds having dark green leaves were selected. For grafting, cleft grafting method was used. After grafting, the union points were firmly wrapped with transparent polyethylene plastic and left until the union was healed and new shoot emerged from the scion shoot.

2.5.2. Data collection

Morphological growths such as new flush bud from the tip, new shoot development from the bud, shoot elongation, scion diameter at union point and numbers of leaves per plant were recorded at a 2-week interval. Physiological parameters such as photosynthesis μmol m⁻² s⁻¹ (A), transpiration rate (E), stomatal conductance (g_s) and water use efficiency were estimated from three randomly selected seedlings from third young, and fully expanded leaves were measured from three randomly selected plants by using a CIRAS-3 portable photosynthesis system (CIRAS-3 PP system Inc., Lincoln, NE, USA). It was measured at 45 days after the actual moisture treatment was imposed on fully developed, intact leaves. Measurements were done between 9:30 AM and 12:30 PM by maintaining the following specifications: leaf surface area at 6.25 cm², ambient CO₂ concentration of 386 µmol mol⁻¹, leaf chamber mass flow rate of 251 µmol s⁻¹, atmospheric pressure of 840 bar and manually fixed photosynthetic active radiation (PAR) to 600 µmol m⁻² s⁻¹.

3. Result and discussion

3.1. Characteristics of the soils media composition used for the pot experiment

The laboratory analysis indicated that the composite soil used for the experiment is loam sandy in texture with pH value of 6.5, which was very mild acidity in nature; its organic carbon content was 3.47% and was having 0.18% total nitrogen (Table 2).

Table 2. Physico-chemical characteristics of the soils media composition used in the pot experiment

Soil properties	Values obtained
Sand%	76
Silt%	20
Clay%	4
Textural class	Loam sandy
pH	6.5
Organic carbon (%)	3.47
Total nitrogen (%)	0.18
Available phosphorus (ppm)	10.8
Field capacity (FC = v/v %)	31.56
CEC (meq/100 g soil)	33

3.2. Morphological growth parameters

3.2.1. New bud break and shoots elongation

The analysis of variances indicated that avocado race and waterlogging stress affected all morphology parameters. New flush bud, new shoot development on scion and new sucker growth on rootstock were significantly (P ≤ 0.05) influenced by the main effect of avocado race and waterlogging stress (Table 3). Mexican race produces lower new leaf flush and new shoot but higher new sucker on rootstock irrespective of waterlogging stress. Guatemalan race subjected to waterlogging stress produces the highest percentage of new flush leaf and new shoot elongation on scion, but is lower in new sucker growth on rootstocks (Table 3), suggesting that Ettinger has a strong potential to downregulate the emergence of new sucker on Guatemalan rootstock than on Mexican rootstock. This might be due to higher concentration of indigenous plant growth hormones like Auxins, and Gibberellins, in the Ettinger scion which involved a strong apical dominance to suppress the development of new shoot below the union or suppress the biosynthesis of cytokinin which has a strong influence on induction of new branch after the apical dominance is decapitated in most plant species (Aloni et al., 2010). The mobile nature of the aforementioned endogenous hormones and its ability to translocate in grafted parts are also expected to contribute in the reduction of sucker development in rootstock (Table 3). However, Nanda and Melnyk (2018) reported that auxins are the main hormones that regulate the growth and development of vascular tissues and their crosstalk with other hormones. In this study, the result could be due to the fact that waterlogging stress inhibits cell division, cell growth and developmental process of the rootstock that may depend on the avocado race type (genetics) and moisture stress level. The result was also supported by Tsering Dolkar et al. (2018) who reported that rootstocks have the potential to regulate and induce the number of buds developed on scion. The reduction in number of new bud flush, new shoot on scion and new sucker on rootstock might be due to the negative effect of lower and excess moisture level on sucker development (Table 3), and this is in line with Frey et al. (2003) who reported that drought, waterlogging, disease and nutrient difference have negative effect on sucker growth.

Table 3. Main effect of waterlogging level and avocado races on avocado scion and rootstock growth and development

Treatments	New bud flush (count)	New shoot on scion (count)	New sucker on rootstock (count)
Waterlogging stress level at (FC)
50%	3.12^a	3.41^a	3.00^b
75%	3.58^a	3.91^a	3.50^a
100%	1.41^b	2.08^c	1.83^c
LSD	0.48	0.49	0.44
Avocado race
Gutamelan	2.92^a	3.61^a	2.22^b
Mexican	2.44^b	2.67^b	3.33^a
LSD (P ≤ 0.05)	0.39	0.49	0.36
CV (%)	14.27	12.45	12.73

Means with different letter in the same column are significantly different at P ≤ 5%, where CV =coefficient of variance, FC =field capacity, LSD =least significant difference.

Similarly, shoot elongation, scion diameter and number of leaves were significantly (P < 0.05) influenced by avocado race and waterlogging stress level, in which maximum shoot tip length, scion diameter and number of leaves were recorded from Guatemalan race at 75% of waterlogging level as compared to the Mexican race. On the contrary, inferior shoot tip elongation, scion diameter and small number of leaves per plant were observed from Mexican race (Table 4) that could be due to variation in dry matter storage in rootstock and inadequate translocation nutrients from root part through the rootstocks to the upper part of the shoot.

Table 4. Main effects of waterlogging and avocado race on shoot tip elongation, scion diameter and number of leaves per plant

Treatments	Shoot elongation (cm)	Scion diameter (mm)	No. of leaves/plant
Waterlogging stress level at (FC)
50%	2.66^a	2.50^b	1.66^b
75%	3.00^a	3.16^a	3.17^a
100%	1.66^b	1.5^c	2.58^b
LSD (P ≤ 0.05)	0.46	0.36	.25
Avocado race
Gutamelan	2.89^a	2.61^a	2.94^a
Mexican	2.00^b	2.17^b	2.67^b
LSD (P ≤ 0.05)	0.38	0.29	.2
CV (%)	15.25	12.08	7.28

Means with different letter in the same column are significantly different at P < 5%, where CV = coefficient of variance, FC = field capacity, LSD = least significant difference.

3.2.1.1. Graft success (%) and rootstock diameter

Analysis of variance showed that graft success percentage and rootstock diameter were significantly (P < 0.05) influenced by avocado race and waterlogging stress level imposed by different watering intervals. However, the interaction of avocado race and waterlogging stress level did not show significant (P > 0.05) difference on graft success percentage and rootstock diameter (Table 5). The highest graft success percentage and the thickest rootstock diameter were recorded from Guatemalan race at 75% waterlogging level as compared to the Mexican race. The lower rootstock diameter was recorded from Mexican race at 100% (Table 5). The highest success percentage in rootstock race might be due to successful graft compatibility of scion with rootstock. The result is in line with Hartmann et al. (2011) who reported that the sequence in grafting regulated with the success of graft union which directly related with the cambial development at the point of contact and rate of cell division, cell elongation and cell differentiation and forming a continuous cambial connection between rootstock and scion. Similarly, it was observed that the more the waterlogging increases, the number of rootstock dry out significantly increased under higher waterlogging condition than plant grown on 50% and 75% moisture level (Table 5). This might be due to oxygen deficiency at root zone under higher moisture level. Previous report by Zhang et al. (2021) also indicated that tissue damage in cotton was mainly due to oxygen deficiency, hypoxia or anoxia as a result of waterlogging around root zone.

Table 5. Main effects of waterlogging and avocado race on number of dried rootstock, graft success (%) and rootstock diameter

Treatments	Number of dried rootstock	Graft success percentage (%)	Rootstocks diameter(mm)
Waterlogging stress level at (FC)
50%	1.67^b	92.83^ab	2.66^a
75%	2.00^b	97.16^a	3.16^a
100%	2.75^a	90.62^b	1.50^b
LSD (P ≤ 0.05)	0.29	3.77	0.46
Avocado race
Gutamelan	2.00^a	94.25^a	2.94^a
Mexican	2.27^b	92.83^b	2.67^b
LSD (P ≤ 0.05)	0.24	3.08	0.38
CV (%)	11.02	3.21	15.25

Means with different letter in the same column are significantly different at ≤ 5%, where CV = coefficient of variance, FC = field capacity, LSD = least significant difference.

3.2.2. Physiological parameters

3.2.2.1. Photosynthesis (A), transpiration (E) and stomata conductance (g_s)

Among the physiological parameters, photosynthesis, transpiration and stomatal conductance of the grafted avocado seedling were significantly affected by avocado race, waterlogging level and interaction of the two factors. Table 6 indicates that the Guatemalan race underwent the highest photosynthetic rate at 75% waterlogging level. The least photosynthetic rate was recorded from 100% waterlogging level which was irrigated in daily basis throughout the experimental period. The result indicates that both genetic and environmental factors are detrimental for the photosynthetic rate where vigorous vegetative growth, elongated shoot and maximum leaf number of the seedling were recorded from Guatemalan than Mexican race at every waterlog stress level (Table 5). The result indicated that variability among race for the rate of photosynthesis is narrowed down under waterlogged conditions. Similarly, the highest transpiration rate recorded from Guatemalan race at 75% waterlogged level compared to the Mexican and the smallest transpiration rate observed at 100% waterlogging level with regard to stomata conductance, the study revealed that watering at 2-day interval (75% waterlogged level) out score at all waterlogging levels in stomata conductance from Guatemalan race and the smallest stomatal conductance was recorded from 100% waterlogging level (Table 6).

Table 6. Interaction effect of avocado race and waterlogging stress level on photosynthesis (A), transpiration rate (E) and stomata conductance (gs)

Avocado race	Waterlogging stress level (%)	Photosynthesis rate (μm)	Transpiration rate (mmol/mol)	Stomata conductance (mmol)
Guatemalan	50	12.00^b	5.5^b	127.33^b
	75	16.00^a	7.30^a	174.00^a
	100	8.63^c	3.93^c	104.67^c
Mexican	50	5.5^d	2.83^d	98.33^d
	75	8.63^c	3.36^cd	104.67^c
	100	4.33^d	1.76^e	77.00^e
CV (%)		10.22	12.83	2.41
LSD at 5%		1.67	0.93	4.89
Significance level		**	**	**

Means with different letter in the same column are significantly different at P < 5%, where CV = coefficient of variance, FC = field capacity, LSD = least significant difference.

Comparable result is also reported by Reeksting et al. (2014) who reported that waterlogged or oxygen-deficient plant had lower leaf gas exchange, net CO₂ assimilation rate (PN), stomatal conductance (gs), transpiration (E), and ratio of internal atmospheric CO₂ concentrations (Ci/Cα) reduced PSII efficiency and water and nutrient uptake restrictions than plant grown under optimum soil moisture condition (Schaffer et al., 1992). A similar report also indicated that low soil oxygen content in avocado orchards resulted in reduction in leaf expansion and root and shoot growth, and lead to severe stem and leaf wilting, leaf abscission and root necrosis (Whiley et al., 2002). Concurrently, Parent et al. (2008), Reeksting et al. (2014) discovered that plants exposed to flooding exhibit increased stomata resistance as well as limited water uptake, leading to internal water deficit. Furthermore, low levels of O₂ may decrease hydraulic conductivity due to hampered root permeability, while the oxygen deficiency leads to a substantial decline in net photosynthetic rate (Ashraf et al., 2012). This decrease in transpiration and photosynthesis is attributed to stomata closure (Ashraf & Arfan, 2005) that hampers most of the physiological functions in plants.

3.2.2.2. Water use efficiency

Avocado race and waterlogging stresses as well as its interaction significantly (P < 0.05) influenced water use efficiency of grafted avocado seedling. Like other physiological parameters, highest water use efficiency was observed from 75% waterlogging stress from Guatemalan race. On the other hand, the lowest water use efficiency was recorded at 100% of waterlogging level from Mexican race (Figure 2). As the soil of the experiment was 76% sandy in proportion the 50% waterlogging or watering at 4-day interval did not well responded to all morphological and physiological parameters.

Figure 2. Interaction of avocado rootstock race and moisture stress level on water use efficiency of seedling rootstock.

Higher photosynthetic character of the Guatemalan race contributes for more water use efficiency as water use efficiency is calculated from the ratio of photosynthesis and transpiration rate. This suggested that Guatemalan race was more efficient to utilize the moisture, producing more dry matter as compared to Mexican race under waterlogging condition through reduction in transpiration rate and maximizing the rate of carbon gain. However, the reduction in WUE in Mexican race is possibly because of the downregulation of transpiration rate and increasing the rate of photosynthesis. Previous report indicated that water use efficiency (or transpiration efficiency) is higher when water evaporation from the interstitial tissues of leaves is higher than the CO₂ acquisition through stomata opening (Bramley et al., 2013).

4. Conclusion

Despite the suitable agro-ecological conditions to grow avocado and its economic importance, the production and quality of avocado produced decrease from time to time due to different biotic and abiotic factors in the tropical environment. The humid tropical environment waterlogging stress has a considerable impact on avocado seedling growth and physiological performance. So far, different breeding activities undertaken provided significant improvements in terms of yield under waterlogging stress for many fruit crops. However, in case of avocado seedling, response to waterlogging stress especially on grafted avocado seedlings is very limited. Therefore, the current study was undertaken to evaluate the morphological and physiological performance of grafted avocado seedling under different waterlogging stress conditions using two rootstock avocado races. The result indicates that the morphological growth of Guatemalan avocado race grafted seedling outscored in number of bud development, shoot growth, rootstock elongation, scion and shoot tip growth compared to Mexican. Similarly, the physiological performance such as photosynthesis, transpiration and stomata conductance of grafted avocado seedling was significantly affected by race, waterlogging level and interaction of the two factors, in which the Guatemalan race performed better nearly in all of the physiological parameters (photosynthesis, transpiration, stomata conductance and water use efficiency) at 75% waterlogging level. On the other hand, the smallest transpiration and water use efficiency were recorded at 100% waterlogging level from the Mexican race. This might be due to poor growth of shoot in Mexican avocado race, because rooting hormones are developed in the shoot part and translocate to the root part of the plant. From waterlogging treatment, significant morphological and physiological performances such as photosynthetic rate, transpiration rate, stomata conductance and water use efficiency were observed from Guatemalan race at 75% waterlogging level. As about 76% of the soil used for the experiment was sandy in proportion, 50% waterlogging level responds less as compared to 75% waterlogging level (2-day irrigation interval). This revealed that the 4-day irrigation interval (50% waterlogging) cannot retain optimum moisture for efficient growth and physiological process. The study revealed that for avocado rootstock propagation, using seedling Guatemalan race as rootstock may give vigorous seedling compared to the Mexican race. Among the different waterlogging levels, better morphological growth was recorded from 75% waterlogging level in loam sandy soil texture that used for the experiment. In conclusion, the study revealed that the avocado rootstock of Guatemalan race performed well at 75% waterlogging condition in loam sandy soil and it can be a potential rootstock in waterlogging soil condition. However, to reach a conclusive recommendation, the experiment needs to be repeated with various avocado cultivars and more waterlogging stress levels.

Data accessibility

All relevant data that supporting the results or analysis presented in this study can be obtained from the corresponding author on request.

Acknowledgments

The authors are very grateful to GIZ-Ethiopia for financing the project and facilitating the field experiment on their nursery site at Tefer-kela. The authors also appreciate Hawassa University College of Agriculture for their smooth finance management and overall support during the course of field experiment.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors received direct financial support from GIZ-Ethiopia.

Notes on contributors

Alemu Dessa Derebe

Alemu Dessa Derebe (PhD, Assistant Professor in Plant Physiology) is professionally a plant physiologist; most of his work is focused on stress physiology and climate change adaptation mechanism. Most of his research work is on plant's adaptation mechanism to different environmental stresses that are induced due to climate change on different horticultural crops including vegetables, tropical fruits and root and tuber crops. So far, the environmental stresses that the author deals with are plant signaling to stress induced by UV-B radiation, moisture stress and nutrient imbalances.

Merzu Weyuma Dema

Merzu Weyuma Dema is an MSc (Horticulture) student attached to a mega project ”Avocado fruit vegetative propagation and reproductive study” for his thesis research under major co-supervision of the first and third authors.

Amsalu Gobena Roro

Amsalu Gobena Roro (PhD, Associate Professor in Plant Physiology) is a senior researcher of plant physiology and leader of the Avocado Research Project at Hawassa University, which is funded by GIZ-Ethiopia.