Resistance of mango (mangifera indica l.) genotypes to anthracnose (colletotrichum gloeosporoides penz.) disease in Uganda

Abstract

Mango (Mangifera indica L.) is an important fruit tree that is grown in tropical and subtropical regions of the world for food and income. Despite its importance, mango production is constrained by anthracnose (Colletotrichum gloeosporiodes) that can cause 60-100% yield loss. The objective of this study was to determine the genetic diversity among landraces and improved mango genotypes in Uganda and determine the levels of resistance to anthracnose among landraces and improved mango genotypes in Uganda. Leaf tissue was sampled from 94 mango genotypes for genotyping using SNP markers generated with DArTseq technology. The AMOVA and cluster analysis revealed significant genetic variation (P<0.001) and three distinctive groupings based on countries of origin was found among the mango genotypes. This is useful genetic resources for exploitation in breeding program against diseases and improving market related traits like yield. In addition, the 94 mango genotypes were grafted with Kagogwa mango rootstock, and six plants per genotype was used in grafting experiment in the screenhouse. The resulting plantlets were then set in randomized complete block design (RCBD) with three replications. Each replication was allocated two plants per genotype in a screen house and infected using artificial inoculation method. The grafts were spray inoculated at 30 days after grafting with purified and 106 spores per microliter of waters (1x106spores/ml) standardized suspension of Ugandan virulent Colletotrichum gloeosporiodes inoculum on the leaves of the plants. Data were collected for six weeks on number of leaf spots, lesion diameter and finally, the anthracnose disease severity score was derived from the number of leaf spots per plot on the scale of 0-5. ANOVA was used to determine the variations in the disease severity score means that were later used to generate AUDPC values to determine disease progression over the six weeks. There was significant (P<0.001) variation in the disease severity scores and AUDPC values among the mango genotypes. Results showed that none of the mango genotypes were completely resistant to mango anthracnose disease. While 8 (9%) genotypes were moderately resistant, 24 (26%) genotypes were moderately susceptible, 59 (63%) genotypes were susceptible and 3 (3%) genotypes were highly susceptible. The moderately resistant mango genotypes recorded in the study were: Ap03, Li01, Se06, Wa15, Li04, Wa30, Yu13 and Li03. Much as, moderately resistant mango genotypes identified in this study can be used in breeding program for developing varieties adapted to the country against mango anthracnose. There is need to screen the moderately resistant genotypes of other plant parts such as flowers, panicles and fruits reported in this study. Future research on the studied mango genotypes needs to adopt molecular screening to determine the resistance level at genetic level.