Evaluation of groundnut (Arachis hypogaea L.) lines for adaptability and reaction to rust disease

Abstract

Groundnut (Arachis hypogaea L.) is an important food crop in Uganda because of its high protein and oil content. Although a wide phenotypic diversity has been observed within cultivated groundnut, the genetic diversity observed to date within the cultivated gene-pool is much lower. Low genetic variability enhancing yield as well as disease resistance traits has been cited as one of the reasons for little progress in groundnut genetic improvement. With climate change, groundnut production constraints such as diseases and pests are likely to be aggravated. Even diseases and pests which are currently of less economic importance could likely become more detrimental with climate change. Groundnut rust is common in countries with warmer, tropical climates but however envisaged to become a major production constraint in Uganda. Yield losses of up to 70% have been reported in field with co-infection of rust and late leaf spot. Like most plant diseases, the use of host resistant is a sustainable way to curb the rust disease among resources poor farmers. However, no breeding effort has been directed at rust resistance in Uganda. Also, exploration of potential areas for expansion of groundnut production is important to exploit the importance of the crop. However, effort to expand groundnut production to new areas such as mid-altitude to highland areas might come with new challenges from erratic diseases like groundnut rust. The objectives of this study were to evaluate 20 groundnut lines resistant to rust for good (agronomic yield) trait, and response to rust in different environments and the variability of the Puccinia arachidis, pathogen responsible for groundnut rust disease. The field experiments were laid out following a randomized complete block design, with two replications at each environment using 20 genotypes including three local checks. Results showed a GxE interaction occurred for most traits except number of pods per plant and 75 DAP. ICGV-SM 15557 was the most stable line for yield across all location. Kalengyere and Buginyanya showed late maturity possibly due to the low temperatures. Highest yield (2018 kg/ha) was recorded at Buginyanya. The Virginia types were most favourable for yield at Buginyanya. The Virginia types were found to be resistant (1-3) and moderately resistant (4-6) to the rust disease. Rust was not observed at high altitudes possibly due to the low temperatures as opposed to the low altitude that showed a relatively higher severity. High late leaf spot (LLS) severity was recorded at Buginyanya. The AMOVA showed no significant difference within the populations for both translocation elongation factor (TEF) and Cytochrome b. TEF showed 21% variation among the population and 79% variation within the population uredospore isolates. Cytochrome b showed no variation among the populations and 100% variation within the populations sampled. Among the populations, PhiPR recorded no value of variation for both TEF and Cytochrome b. This study shows that groundnut production can be expanded to non-traditional areas like Buginyanya possibly with genotypes resistant to LLS. The rust resistant genotypes used in this study can be utilized in Uganda either as released varieties or as parents for introgressing rust in farmers preferred groundnut cultivars. Genotypes somehow escaped rust with very low severity due to the environmental conditions in the other environments. No new strain of rust was found in Uganda in this study.