Genotype � environment interactions in symptom development and yield of cassava genotypes with artificial and natural cassava bacterial blight infections

Abstract

Thirty-seven cassava genotypes from Benin, including advanced breeding lines, were tested for their reaction to bacterial blight in the forest-savanna transition, wet savanna and dry savanna zones of Benin. Sixteen genotypes were repeated in 12 environments. In year 1998, genotypes RB92164, RB92022, TMS30572, BEN86004, RB92033 and Dangbo2, and in year 2000, genotypes RB92202, RB92151, RB92132 and TMS30572 were resistant in one ecozone. Among the more resistant genotypes, CAP94030, BEN86040, RB89509, RB92132 and TMS30572 showed low interaction across environments and were most stable in disease reaction. Ten genotypes were classified as high yielding across environments. Among the more resistant group of genotypes, only TMS30572 and RB89509 were high yielding, with RB89509 being unstable in yield across environments. Selection of genotypes proved reliable only after artificial inoculation. Comparing environments, artificially inoculated treatments in the wet savanna zone and in the forest-savanna transition zone with stable high symptom severity proved most suitable for screening of genotypes, while the wet savanna zone with low natural infection in year 1998 was suitable for production of propagation material, and the site in the dry savanna zone with natural infection in year 1998 was the best environment for cassava production. The correlation between disease severity and root yield was significant only for the non-inoculated treatment in the dry savanna zone in year 2000 (R ¼ )0.58), but not in any other environment. Among the 37 genotypes tested, several genotypes can be recommended to farmers in specific ecozones, and genotype TMS30572 revealed as relatively stable in disease resistance and in high yield across ecozones.

Leaf Waxes of Cassava (Manihot Esculenta Crantz) in Relation to Ecozone and Resistance to Xanthomonas Blight

“…For wax analysis The fourth leaf from the top was collected from randomly selected 11 months-old cassava plants of genotypes BEN86052 and TMS30572, and of genotypes RB92132, CAP92034, CAP94030, RB92004 and BEN86040 (moderately) resistant to cassava bacterial blight (Zinsou et al, 2005), with five leaves per genotype and three replicates.…”

“…In previous studies (Zinsou et al, 2005), these genotypes were evaluated for numbers of leaves with spots or blight, dropped/wilted leaves and stems with dieback symptoms at a monthly interval with a gap over the dry season. The severity index in days over 12 months was calculated according to the following formula:…”

“…In field trials in Togo, Benin and Nigeria as well as under controlled conditions the standard resistant genotype TMS30572 constantly produced less symptoms than susceptible genotypes across ecozones and years (Fanou, 1999;Banito, 2003, Zinsou et al, 2005, Wydra, 2002. Host plant resistance in cassava is described as polygenic and additively inherited, deriving from interspecific cross-breeding between M. esculenta and the wild relative M. glaziovii (Hahn et al, 1979).…”

Cassava Bacterial Blight: A Devastating Disease of Cassava

“…In our study, the results reveal the narrow basis for resistance to bacterial blight in local improved cassava varieties from Benin. Considering disease reaction and root yield across environments, only genotype TMS30572 was consistently moderately resistant to resistant and high-yielding in different environments [88]. Thus, genotype TMS30572 can be recommended to farmers.…”

“…Our results in Benin showed that differences in environmental conditions may have an influence on wax quantities and thereby, contribute to the high genotype x environment interactions in cassava [88]. Stomatal anatomy was reported to confer resistance to some varieties against certain of their bacterial pathogens [92].…”