Variation in nectar volume and sugar content in male flowers of Musa cultivars grown in Rwanda and their non-effect on the numbers of visiting key diurnal insect vectors of banana Xanthomonas wilt

Abstract

Insects are a major mode of banana Xanthomonas wilt (XW) spread. High insect activity has been blamed for the high XW incidence in 'Kayinja' (ABB-genome) dominated banana landscapes across east and central Africa. 'Kayinja' male bud nectar composition reportedly contributes to high insect activity. The variation in nectar composition with agro-ecological zones and banana cultivars and its influence on the number of visiting insects in Rwanda were assessed. Three male buds were collected per cultivar for nectar extraction and analysis using a high performance liquid chromatography. Nectar volume and sugar concentrations varied (P<0.001) across 27 banana cultivars, annual seasons and agro-ecological zone. The highest nectar volume was recorded among the East African highland cooking cultivars (AAA-genome) in the high altitude site and the short-heavy rainy season. Nectar contained three sugars: glucose, fructose and sucrose, though hexose (glucose and fructose) was dominant. The three sugars varied significantly (P<0.001) within each cultivar. The total nectar-sugar concentration ranged from 2.3-32%, with the highest among dessert cultivars 'Kamaramasenge' (AABgenome) and 'Gisukari' (AAA-genome). No strong correlation occurred between insect population and total nectar sugar concentration or nectar volume. Insect populations were rather influenced by the weather conditions, the long rainy season characterized by moderate well distributed rainfall recording the highest insect populations as compared to the short rainy season (with heavy rainfall) and the dry seasons.

Bacterial Diseases of Bananas and Enset: Current State of Knowledge and Integrated Approaches Toward Sustainable Management

“…As a result, cultivars like Cavendish (AAA) and Lakatan (AAA), are not seriously affected by Bugtok under small-scale farmer conditions because insects do not prefer to feed on these varieties (Molina, 2006). More recent findings in Xanthomonas wilt affected zones revealed that though insect populations play an important role in disease spread, the observed high susceptibility of ABB or BBB cultvars is attributed to their non-persistent male and neutar flowers and bracts (Addis et al, 2004; Shimelash et al, 2008; Ocimati et al, 2013a; Rutikanga et al, 2016b). These male and neutar flowers/bracts leave behind fresh open wounds that act as entry points for the pathogen(s) on the body parts of visiting and foraging insects…”