Effect of canopy temperature on the stripe rust resistance of wheat

Abstract

Stripe rust of wheat (Triticum aestivum), caused by Puccinia striiformis f. sp. tritici, is highly affected by temperature, but the role of crop canopy temperature in stripe rust resistance is poorly understood. Five wheat varieties, which have different canopy temperatures and are susceptible to P. striiformis f. sp. tritici at the seedling stage, were investigated for resistance to stripe rust at the adult-plant stage in greenhouse and field experiments. In the greenhouse tests, all five varieties were resistant to stripe rust at the adult-plant stage. At the grain-filling stage in the 2007–2010 field experiments at two locations, the two varieties (NR 9405 and 9430) with higher canopy temperatures had lower disease index and smaller area under the disease progress curve values than the three varieties (Shaan 229, RB 6 and Xiaoyan 6) with lower canopy temperatures. The results indicated that the five tested wheat varieties had similar resistance reactions to stripe rust at the adult-plant stage in the greenhouse experiment, but showed different levels of resistance under natural infection conditions in the field. The negative correlation between canopy temperature and disease index during the grain-filling stage was significant. Thus, high wheat canopy temperatures provide unfavourable conditions for the development of stripe rust. This study is helpful for further developing an ecological approach for reducing stripe rust damage.

Keywords:

• canopy temperature
• Puccinia striiformis f. sp. tritici
• resistance
• stripe rust
• Triticum aestivum

Introduction

Interactions between plants, the soil and the atmosphere are reflected by crop canopy temperatures (Feng et al. 2009). Previous studies have demonstrated that the canopy temperatures of wheat varieties can be different under similar climatic, soil and farming conditions during the heading, anthesis and, more noticeably, grain-filling period, which is a key period for kernel formation (Zhang 1990, 1997; Fischer et al. 1998; Zhang & Wang 1999a,b). Some researchers have found that many other crops also exhibit differences in canopy temperature, including rice, soybean, peanut, corn, cotton and peas. Crops with low canopy temperatures have superior physiological characteristics, such as leaf functional duration, chlorophyll content, activities of superoxide dismutase, protein content, transpiration rate and high net photosynthesis rate (Kirkham et al. 1984; Hatfield et al. 1987; Han et al. 2007; Li et al. 2007; Ren et al. 2008; Wang et al. 2009). Therefore, low canopy temperatures in crops may provide a broad developmental advantage with respect to production.

The concept of low-temperature wheat (LTW) was first proposed in 1996 (Zhang et al. 1996). If the canopy temperature of a wheat variety is constantly lower than that of a control (e.g. Xiaoyan 6, a predominant variety in local wheat production) during the grain-filling period, the wheat variety is considered as LTW. Conversely, it is considered as high-temperature wheat (HTW). Differences in canopy temperature among some wheat varieties can reach 4 ^oC at midday on a sunny day (Zhang et al. 1996). Wheat temperature types remain similar across years and under different weather conditions (Zhang 1997; Zhang & Wang 1999a,b).

Wheat varieties with low canopy temperatures are reported to have superior physiological and metabolic aspects (Zhang 1990, 1997; Zhang & Wang 1999a,b; Feng et al. 2001, 2002, 2009; Ayeneh et al. 2002), grow well and have high water utilisation rates (Pinter et al. 1990; Fischer et al. 1998). These characteristics help to delay leaf senescence, extend the grain-filling period and increase yield (Van Ginkel et al. 2004), in addition to enhancing resistance to drought, waterlogging and heat stress (Amani et al. 1996; Rashid et al. 1999; Xu et al. 1999; Zhang et al. 2001, 2004; Ayeneh et al. 2002). However, no studies have been conducted on the effect of canopy temperatures on stripe rust resistance.

Stripe rust of wheat (Triticum aestivum L.), caused by Puccinia striiformis Westend. f. sp. tritici Erikss., is one of the most serious foliar diseases of wheat worldwide (Stubbs 1985; Chen 2005; Wellings 2011). Wheat yield reduction caused by stripe rust may reach 75% in severe epidemics in susceptible varieties (Roelfs et al. 1992; Chen 2005, 2014; Wan et al. 2007). In China, 4 million hectares of wheat may be affected by stripe rust annually (He et al. 2011). Therefore, it is important to grow varieties resistant to the disease. Adult-plant resistance is often preferred to seedling resistance as it is generally more durable (Chen 2005). However, adult-plant resistance is often under the influence of temperature and may not be effective when temperatures are low. Understanding the effect of canopy temperature on stripe rust resistance may improve breeding for resistance by selecting varieties with preferred canopy temperatures.

In this study, five wheat varieties with different canopy temperatures were investigated for resistance to stripe rust in greenhouse and field experiments. The objective of this study was to determine the effect of canopy temperature on the stripe rust resistance of wheat. The results of the study may provide a basis for further development of an ecological approach to reducing stripe rust damage.

Materials and methods

Plant materials

Five wheat varieties were selected based on canopy temperatures reported in previous studies (Zhang et al. 1996; Zhang 1997; Zhang & Wang 1999a,b, 2001; Xu & Zhang 2000, 2002a; Miao et al. 2003). NR 9405 and 9430 were chosen as HTW varieties; and Shaan 229, RB 6 and Xiaoyan 6 as LTW varieties. Xiaoyan 6 also served as a control for disease resistance as it is a major wheat variety grown in Shaanxi province, where the field experiments were conducted.

Pathogen isolates

Two Chinese races of P. striiformis f. sp. tritici, CYR29 and CYR32, which are predominant races in China (Wang et al. 1995; Wan et al. 2007), were used in the greenhouse experiment. Urediniospores of the races obtained from the College of Plant Protection, Northwest A&F University, were multiplied on susceptible wheat variety Mingxian 169 in a growth chamber for production of fresh urediniospores. For field experiments, stripe rust was established by natural infection.

Greenhouse experiments

For the greenhouse experiments, germinated seeds of wheat varieties were vernalised at 4 °C for 40 days. Seedlings were transplanted into a 15 (height) × 15 (diameter) cm clay pot (four plants per pot) and grown in a rust-free greenhouse. The seedlings were uniformly inoculated with urediniospores of a selected race mixed with talcum (1:20) during the booting to heading period. Inoculated plants were placed in a dew chamber at 10 °C in the dark for 24 h and then divided into two groups. One group was grown in a greenhouse at a low-temperature (LT) cycle (10 ^oC at night and 15 ^oC in the day) and another group was grown at a high-temperature (HT) cycle (14 ^oC at night and 34 ^oC in the day), simulating the natural temperature ranges during the early and late growing seasons in the Huanghuaihai winter wheat areas in China. Both greenhouses were set with the same photoperiod cycle (16 h light/8 h dark). Wheat variety Mingxian 169, which is highly susceptible to stripe rust in both seedling and adult-plant stages, was tested with the same race at the same time as a susceptible control in the greenhouse. Infection type (IT) data were recorded twice at 18 and 21 days after inoculation for both temperature cycles on a 0–9 scale (Line & Qayoum 1992). The experiment was repeated three times with each treatment being replicated three times for each experiment.

Field experiments

Experimental design

Field experiments were conducted for 4 years at two locations, Luojia village (107.67°E, 34.26°N) (2007–2009) and Xishilin village (107.9°E, 34.2°N) (2010), Baoji, Shaanxi Province, China. The locations were in the Huanghuaihai winter wheat region, one of the most important wheat production regions in China with a warm and semi-humid climate.

A randomised complete block design with three replications was used for the field experiments. Each plot was 5 × 5 m in length and width with spaces of 0.2 m between rows. Plots were spaced 0.5 m apart. Seeds were sown at a rate of 14 g per 5 m row in early October of each year, which is the optimal planting period at these locations. Xiaoyan 6, Shaan 229 and NR 9405 were used in the field experiments in 2007 and 2008, whereas RB 6 and 9430 were added to the field experiments in 2009 and 2010. Wheat variety Xiaoyan 22 was planted around the experimental field to form a buffer zone in all 4 years. The field plots were managed according to the common practices in the Huanghuaihai winter wheat areas in China.

Stripe rust scoring

Stripe rust on wheat plants was assessed on the same leaf position at each of five time points. The total numbers of plants and leaves were recorded for two neighbouring 1 m rows. The numbers of diseased plants and leaves and disease severity were recorded five times at about 7-day intervals from the booting to the grain-filling stage. Severity was recorded as the percentage of the lesion area in the total leaf area and was generally divided into eight categories: 1%, 5%, 10%, 20%, 40%, 60%, 80% and 100%. The disease ratio, disease index and area under the disease progress curve (AUDPC) and were calculated (Momol et al. 1990; Xu et al. 2004) using the following formulae:(1) (2) (3)

where X_i and X_i+1 are the disease severity values at ith time and (i + 1)th time, respectively, and (T_i+1−T_i) is the interval between two consecutive assessments.

Measurement of the canopy temperature

Canopy temperatures of the wheat varieties were measured five times at sunny noontime at 5-day intervals for all plots during the grain-filling stage in the field experiments. A BAU-I infrared temperature measurer (CAU, Beijing, China) was used to monitor the canopy temperatures. The apparatus was held so as to view the crop at an angle of 30° from the horizontal at right angles to the rows at a distance of 1.5 m above soil surface to minimise the influence of exposed soil (Zhang et al. 1996; Zhang 1997; Rashid et al. 1999; Zhang & Wang 1999b; Zhang et al. 2001; Feng et al. 2009). The canopy temperature value for each plot was the mean of five different spots with three readings at each spot.

Statistical analysis

The data from the different treatments were evaluated by analyses of variance (ANOVA), multiple comparisons and correlation using SPSS (version 19.0 for Windows).

Results

Greenhouse evaluation of stripe rust resistance

The stripe rust infection types of the flag and lower leaves of the five inoculated wheat varieties are shown in Table 1. The highly susceptible control variety Mingxian 169 was highly susceptible (IT 9) to both races under both temperature cycles at the adult-plant stage in the greenhouse study (data not shown). Although the five inoculated wheat varieties had different ITs, all were resistant (IT 0–2) to both races under both temperature cycles.

Table 1 Infection types produced on the flag leaf (top leaf) and lower leaf of five wheat varieties inoculated with Puccinia striiformis f. sp. tritici races at different temperatures during the adult-plant stage.

Race	Wheat variety	IT^a (10–15 °C)		IT^a (14–34 °C)
		Flag leaf	Lower leaf	Flag leaf	Lower leaf
CYR29	Shaan 229	1	1	0	0
	RB 6	1	1	1	1
	Xiaoyan 6	1	1	0	0
	NR 9405	1	1	0	0
	9430	1	1	0	0
CYR32	Shaan 229	1–2	1–2	1–2	1
	RB 6	1–2	1–2	2	2
	Xiaoyan 6	1	1	0–1	0–1
	NR 9405	1	1	1	0–1
	9430	2	1	0	0

IT, infection type.

^aData were recorded 14 days after inoculation. Infection type is based on a scale of 0–9.

A dash (–) indicates a range of infection types on the same plant.

Data are based on 20 plants per treatment with three replications.

Stripe rust resistance in the field

AUDPC

The AUDPC values of the wheat varieties are shown in Fig. 1. In 2007, the AUDPC value of the control (Xiaoyan 6) was 103.87; and the value of Shaan 229 (LTW) (285.38) was significantly higher (P < 0.05) and of NR9405 (HTW) (16.83) was significantly lower (P < 0.05) than that of the control. During 2008–2010, the AUDPC values of both LTW varieties (Shaan 229 and RB 6) were significantly higher (P < 0.05) than those of the control, whereas those of the two HTW varieties (NR 9405 and 9430) were significantly lower (P < 0.05). No significant differences in AUDPC were found between wheat varieties with similar canopy temperatures.

Figure 1 The area under the disease progress curve (AUDPC) of five wheat varieties in field trials spanning 4 years (2007–2010). The data are the mean value of five points with three replications. Different letters indicate a significant difference at P < 0.05 among the different wheat varieties in each year, according to Tukey's multiple comparison. The data variation is given as the standard deviation (SD) of the mean.

Disease index

During the grain-filling stage in 2007, the disease indices of Shaan 229 (LTW) and NR9405 (HTW) reached 20.96 and 1.03, respectively, whereas that of the control (Xiaoyan 6) was 3.24 (Fig. 2). During the grain-filling period of 2010, the disease indices of Shaan 229 and RB 6 (LTWs) reached 17.19 and 13.28, respectively, whereas those of NR 9405 and 9430 (HTWs) were only 0.62 and 0.67, respectively, and that of Xiaoyan 6 (control) was 3.51. The ranking of the disease indices were similar, as they were highest for the LTWs, followed by the control and the HTWs in 2008 and 2009.

Figure 2 Disease indices of five wheat varieties at the grain-filling stage in field trials spanning 4 years (2007–2010). The data are the mean values of five points with three replications. Different letters indicate a significant difference at P < 0.05 among the different wheat varieties each year, according to Tukey's multiple comparison. The data variation is given as the standard deviation (SD) of the mean.

The disease index of the control (Xiaoyan 6) increased significantly (P < 0.05) at the heading stage and then slightly increased and peaked at the grain-filling stage. The disease indices of the two LTWs (Shaan 229 and RB 6) significantly increased (P < 0.05) during the heading period, then rapidly increased and peaked at the grain-filling stage. Both LTWs had significantly higher (P < 0.05) disease indices than the control (Xiaoyan 6) from the booting to the filling stage. The disease indices of the two HTWs (NR 9405 and 9430) increased slightly and remained low from the booting to the filling stage. Both HTWs had significantly lower (P < 0.05) disease indices than the control (Xiaoyan 6) on all recording dates in all 4 years (2007–2010) (Fig. 3).

Figure 3 Changes in stripe rust disease index of five wheat varieties in field trials in A, 2007; B, 2008; C, 2009; and D, 2010. The data are the mean values of five points with three replications for each plot. The data variation is given as the standard deviation (SD) of the mean.

There were significant differences in AUDPC and disease index values at the grain-filling stage among the three tested wheat varieties (Shaan 229, Xiaoyan 6 and NR 9405) in the 2007 and 2008 field experiments. The LTW wheat variety, Shaan 229, had significantly higher AUDPC and disease index values at the grain-filling stage than the control (Xiaoyan 6) and the HTW (NR 9405) in the 2-year field experiments. In 2009 and 2010, RB 6 and 9430 were added to the field experiments. The results showed that LTW varieties (Shaan 229 and RB 6) had significantly larger AUDPC and disease index values than the control (Xiaoyan 6) and the HTW varieties (NR9405 and 9430) at the grain-filling stage.

Measurement of the canopy temperature

The differences in canopy temperatures in the five wheat varieties during the grain-filling stage in the 2010 field experiment are shown in Table 2. All of the five wheat varieties exhibited different mean canopy temperatures and the levels of difference among the varieties were different. The difference in canopy temperatures among the five wheat varieties during the grain-filling stage was highly significant (P < 0.01). The canopy temperatures of Xiaoyan 6 (the control), Shaan 229 and RB6 were significantly lower than those of NR 9405 and 9430; however, no significant difference was observed between Xiaoyan 6 (the control), Shaan 229 and RB6 during the grain-filling stage. These results were consistent with the observation of the canopy temperatures reported previously (Zhang et al. 1996, 2004; Zhang 1997; Feng et al. 2002). Shaan 229, RB6 and Xiaoyan 6 could be considered as LTW varieties, whereas NR 9405 and 9430 could be considered as HTW varieties.

Table 2 Canopy temperatures (°C) of high temperature wheat (HTW) and low temperature wheat (LTW) varieties during the grain-filling period in 2010.

Variety	Canopy temperature (°C)
	5 May	10 May	15 May	20 May	25May
HTW
9430	23.5a	23.2a	25.7a	25.0a	24.5a
NR 9405	24.6a	23.6a	26.2a	24.9a	24.3a
LTW
Xiaoyan 6	22.6b	22.4b	24.5b	22.8b	22.6b
Shaan 229	22.0b	21.3b	23.2b	22.0b	22.1b
RB6	21.9b	21.8b	23.8b	22.4b	22.0b

The data are the means of five spots with three measures at each spot. Different letters in different genotype wheat varieties indicate significant differences (P < 0.05).

Correlation between canopy temperatures and disease indices

The significant negative correlation between canopy temperatures and disease index values during the grain-filling stage is shown in Table 3. The disease index values of the HTWs (NR 9405 and 9430) were significantly lower than the LTWs (Shaan 229 and RB 6).

Table 3 Regressions between stripe rust disease index (y) and canopy temperature (x) during the grain-filling stage on high temperature wheat (HTW) and low temperature wheat (LTW) varieties.

Variety	Regression formula	R	R^2
HTW
9430	y = 11.106–0.432x	−0.787**	0.619
NR9405	y = 2.402–0.078x	−0.482*	0.232
LTW
Xiaoyan 6	y = 51.867–1.864x	−0.923**	0.853
Shaan 229	y = 349.391–14.603x	−0.917**	0.840
RB6	y = 95.686–3.759x	−0.995**	0.990

*, **Correlation is significant at the 0.05 and 0.01 probability levels, respectively.

Discussion and conclusions

It has been reported that all five tested wheat varieties were highly susceptible to stripe rust at the seedling stage (Cheng et al. 2009), but exhibited resistance at the adult-plant stage in the greenhouse as shown in this study. Consistent with previous reports (Guo et al. 2005; He et al. 2011; Yan et al. 2011), Shaan 229 and Xiaoyan 6 exhibited adult-plant resistance to stripe rust. The present study is the first to show that wheat varieties RB 6, NR 9405 and 9430 also have adult-plant resistance to stripe rust.

All of the five tested wheat varieties had similar resistance reactions to stripe rust at the adult-plant stage in the greenhouse experiment but exhibited different levels of resistance under natural infection conditions in the 4-year field experiment at the two locations. Much of the differences in the fields could be attributed to the differences in canopy temperature.

Previous studies have demonstrated that the micro-environment of fields grown with LTW varieties is cooler and wetter than that of fields grown with HTW varieties (Zhang & Wang 1999b; Xu & Zhang 2000, 2001, 2002a,b). These conditions are caused by various biological characteristics in LTW varieties, including a longer functional period of the leaves, stronger evaporation and bigger root systems. Previous studies have indicated that moisture affects spore germination, infection and survival (Rapilly 1979; Brown & Hovmøller 2002; Line 2002; Wan et al. 2004; Chen 2005). Thus, high moisture causes urediniospores to adhere more strongly to the leaves, with high humidity promoting stripe rust development because this condition favours spore germination, leading to an increased infection frequency. Rapilly (1979) and Line (2002) provided detailed reviews of the effects of temperature on stripe rust. Temperature affects P. striiformis f. sp. tritici spore germination, in addition to infection, latent period, sporulation, spore survival and host resistance. Furthermore, the stripe rust fungus preferentially grows on host crops with relatively cool temperatures. Thus, the moist and cool farmland ecological environments of LTW varieties provide conditions conducive for stripe rust development, especially during late growth. The significant negative correlation between canopy temperature and disease index during the grain-filling stage found in this study indicates a potential for screening wheat genotypes for stripe rust response. Thus, wheat varieties with higher canopy temperatures might provide unfavourable conditions for the occurrence of stripe rust and efficiently alleviate stripe rust epidemics. However, different pathotypes/races of the stripe rust pathogen in the field could contribute to the variation in stripe rust severity. Additional research is needed to check the races and their virulence on the tested varieties. Therefore, further evaluations are needed before using canopy temperature as a screening tool for stripe rust resistance.

This study is the first to investigate the effect of wheat canopy temperature on stripe rust resistance. The present study provides a basis for utilising canopy temperature as a trait for selecting wheat varieties to enhance resistance and improve control of stripe rust.

Acknowledgements

This research was supported by the National Basic Research Programme of China (973) (No. 2013CB127700) and the 111 Project from the Ministry of Education of China (No. B07049). We thank Professor Xianming Chen and Dr Qingmei Han for their critical reviews of the manuscript and to Yinchao Chen and Guorong Wei for assisting with the greenhouse and field experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.