Rapid Screening of Musa Species for Resistance to Black Leaf Streak Using In Vitro Plantlets in Tubes and Detached Leaves

Abstract

This study investigated the utility of inoculation of in vitro plantlets in tubes and detached leaves as reliable and rapid assays for screening Musa genotypes against Mycosphaerella fijiensis, the causal agent of black leaf streak. In the first part of the study, three types of inocula were evaluated to determine suitability for in vitro inoculation. Inoculation of in vitro plantlets with mycelial fragments resulted in significantly (P < 0.05) higher levels of disease severity and faster rates of disease progress compared with inoculations using conidial suspensions. In the detached leaf assay, amending agar medium with plant hormones significantly (P < 0.0001) aided retention of green leaf color. Leaf pieces on medium containing gibberellic acid at 5 mg/liter had about 5% chlorosis at 52 days after plating. When in vitro plantlets in tubes and detached leaves of 10 Musa genotypes with different levels of disease resistance were inoculated with M. fijiensis, there were significant (P < 0.05) differences among genotypes in leaf area infected, incubation time, and symptom evolution time. For incubation time and leaf area infected, cultivars responded depending on their level of disease resistance, with resistant genotypes Calcutta-4 and PITA-17 having significantly (P = 0.001) longer incubation times and lower infected leaf areas compared with the susceptible cultivar Agbagba and moderately resistant cultivar FHIA-23. A similar pattern in cultivar response was observed for symptom evolution time. Leaf area infected was not significantly (P = 0.2817 for two-tailed t test) different when assessed using the two assays, and infected leaf areas in both assays were strongly correlated (r = 0.88, n = 48, P < 0.0001). Although incubation times were significantly (P = 0.0062 for two-tailed t test) different between the two assays, values from the two assays were strongly correlated (r = 0.69, n = 48, P < 0.0001). These results show that these two assays are rapid and space-effective, and can reliably be used for screening Musa genotypes for resistance to black leaf streak.

Expression of a rice chitinase gene in transgenic banana (‘Gros Michel’, AAA genome group) confers resistance to black leaf streak disease

“…During the last decade, these bioassays became a useful tool for screening transgenic plants for disease resistance (Kumar et al 2003; Marchant et al 1998; Takatsu et al 1999). Two main categories of LDA can be distinguished, detached (Abadie et al 2009; Agnola et al 2003; Bussey and Stevenson 1991; Cohen 1993) and attached LDAs (Donzelli and Churchill 2007; Meeley et al 1992; Twizeyimana et al 2007a, b). In case of banana, rapid mass screening with attached leaves is difficult to carry out because of requirements in space and screenhouse conditions (e.g., high humidity and temperature) for efficient control of inoculations.…”

Rapid screening of Musa species for resistance to Fusarium wilt in an in vitro bioassay

“…Considering banana germplasm is often exchanged or released as in vitro conserved plantlets, the bioassay would also have application in assessment of newly introduced accessions. Similar early evaluation methods have been developed for rapid screening of Musa species for resistance to black leaf streak (Twizeyimana et al 2007) and Xanthomonas wilt (Tripathi et al 2008), respectively. …”

A rapid technique for screening banana cultivars for resistance to Xanthomonas wilt

“…Similar early evaluation methods have also been developed for screening Musa spp. for resistance to the fungal disease, black leaf streak (Mobambo et al 1994;Twizeyimana et al 2007). Variation in isolate pathogenicity can influence the value of controlled environment resistance screening but for BXW we found no variation in pathogenicity between the 16 isolates tested on the eight cultivars of banana.…”