Files
Abstract
Fusarium wilt is among the major soil borne fungal diseases hindering sweet potato production in temperate regions of the world. Resistant cultivars are important for commercial production as the impact of Fusarium wilt is aggravating due to intensifying climate variability, thus the need for quick screening methods. The objectives of this study were to test a quick screening method at the early growth stage, to identify resistant parents, and to screen resultant progenies for resistance under glasshouse and field conditions. Virulent isolates of Fusarium oxysporum f. sp. batatas (PPRI15907) and F. oxysporum f. sp. vanillae (PPRI9458) were used. The soil was artificially inoculated and planted with month-old sweet potato plantlets. Visual leaf and stem disease assessments were recorded at 6 weeks after planting using an ordinal rating scale (0–3). Both leaf and stem disease assessment results indicated significant variation (P ≤ 0.05) in the disease reaction of the genotypes. Based on stem disease severity index (DSI) as determined from the quick screening, Bonita (4.2%) and Monate (8.3%) were classified as resistant, and Blesbok (66%) and Lethlabula (81%) as highly susceptible parents. Furthermore, DSI categorized the 92 progenies into 44 resistant, 21 moderately resistant, 13 moderately susceptible, seven susceptible and seven highly susceptible genotypes. The field experiment confirmed that 84% of genotypes that were identified to be resistant to Fusarium wilt under glasshouse conditions, were also resistant under field conditions. Thus the glasshouse method is reliable, efficient, and can screen large numbers of sweet potato genotypes for resistance against virulent Fusarium oxysporum isolates.