The susceptibility of bananas to crown rot disease is influenced by geographical and seasonal effects

Figures & data

Fig. 1. Clusters of bananas divided into two parts through the transverse cutting of the crown for the visualization of internal crown rot symptoms that was adjusted to a rectangular shape for measurements of the necrotic surface.

Fig. 2. Representation of different means of INS versus their confidence intervals at 95% assessed in two experiments differing by their post-inoculation environmental conditions in (a) Dia-dia, (b) Koumba and (c) Ekona. In experiment 1 (Black

) conducted from June 2006 to May 2007, bananas were stored at 13 °C for 10 days to simulate shipment; then artificial ripening was initiated with ethylene and bananas remained at 20 °C for another 3 days before crown rot assessment. In experiment 2 (Grey

) conducted from November 2007 to October 2008, bananas were stored at 13 °C for 13 days. Each point represents the INS of three clusters per harvested bunch. Fifteen bunches were harvested per month in the three locations (Dia-dia, Koumba and Ekona) during 12 months of experimentation.

Fig. 3. Time course of the variation of internal necrotic surface (INS) in Dia-dia (——) and Koumba (-- -- -- --). Each point represents the average mean of three replicates for each location (for each repetition INS was assessed over 15 fruits). Error bars represent standard deviation.

Table 1.  Variance analysis of geographical and seasonal effects on banana susceptibility to crown rot

	Internal necrosis surface (INS)
Source	d.f.	F	P
Location	2	18.70	< 0.001
Season	1	3.93	0.075
Date (Season)	10	8.23	< 0.001
Location * Season	2	2.40	0.111
Location * Date (Season)	20	1.90	0.011
Bunch (Location Season Date)	425	3.97	< 0.001
d.f. is the degree of freedom, F is the value of F test and P is the probability.

Fig. 4. Seasonal variation of the internal necrotic surface (INS —

—) on banana clusters inoculated with a conidial suspension of C. musae (10⁴ conidia mL⁻¹) during one year assessment in (a) Dia-dia, (b) Koumba and (c) Ekona. For each date of harvest, INS is the mean of 15 replicates (bunches) and standard errors are represented by vertical bars. The shaded columns represent the average monthly rainfall.

Table 2.  Mean values and standard deviations of internal necrosis surface (INS), variation values (min – max) of INS, grade, number of hands (NH), number of leaves (NL) and black leaf streak disease (BLSD) severity measured during one year in two lowland plantations (Dia-dia and Koumba) and one highland plantation (Ekona). P is the probability

Location	INS (mm^2)	Grade (mm)	NH	NL	BLSD severity (%)
Dia-dia (80 m–27 °C)	385.8 ± 91.1^a (311–489)	32.7 ± 2.0^x	8.3 ± 1.7^y	8.2 ± 1.8^x	33.0 ± 18.2^y
Koumba (80 m–26 °C)	366.4 ± 94.0^a (287–495)	32.5 ± 2.5^x	7.8 ± 0.7^x	8.3 ± 1.7^x	38.4 ± 18.0^x
Ekona (500 m–22 °C)	313.4 ± 73.1^b (275–368)	37.4 ± 2.6^y	8.2 ± 1.5^xy	9.6 ± 2.1^y	27.6 ± 17.7^z
P	< 0.001	< 0.001	0.006	< 0.001	< 0.001
Note: INS, grade, NH, NL and BLSD severity means was calculated for 12 harvest dates. For each harvest date, 15 bunches were harvested in each location, and three clusters per bunch were inoculated for INS assessment. Data in parentheses are the minimal and the maximal average values of INS observed in the different locations at the different dates. The letters a, b for INS and the letters x, y, z for grade, NH, NL and BLSD severity represent groups of statistically different fruits defined by the Tukey test (5%).