Field resistance of advanced breeding lines of upland cotton to ramulosis caused by Colletotrichum gossypii var. cephalosporioides

Abstract

Cotton ramulosis caused by Colletotrichum gossypii var. cephalosporioides is the main disease in the cotton growing areas of South America. Commercially available cultivars do not exhibit ramulosis resistance and thus it is necessary to identify sources of resistance. This study evaluated the Colombian LCER collection of advanced breeding lines (ABLs) of Upland cotton for ramulosis resistance. LCER is composed of F6 lines derived from crosses between lines with African and Colombian ancestry (LC collection) and high yielding cultivars from USA, Brazil and Africa adapted to the monsoon and savanna climate of the Colombian Caribbean. Disease development was measured thirteen weeks after planting using a qualitative scale designed for high levels of ramulosis intensity (absence of healthy plants and high proportions of dwarf plants for susceptible cultivars). A ramulosis resistant scale (RSC) was developed from these disease assessments to evaluate the ABLs across environments. Thirteen ABLs exhibited ramulosis resistance. Fourteen ABLs were classed as susceptible cultivars, while the remaining 30 exhibited intermediate levels of resistance. Half of the individuals in susceptible ABLs exhibited dwarfism symptoms while the plant population in resistant cultivars showed lower percentage of dwarfism (<1%) and sprouting (around 50%). Thirty seven ABLs representing the range of disease responses were evaluated at a second location. Multifactor ANOVA revealed that resistance measured as RSC scores can be used to evaluate genotypes across environments to identify sources of resistance. These resistant ABLs can be released as new resistant cultivars for the Caribbean or used as parents in breeding programs.