Genetic diversity and population structure of Peronosclerospora sorghi isolates of Sorghum in Uganda

Abstract

Sorghum is the third most important staple cereal crop in Uganda after maize and millet. Downy mildew disease is one of the most devastating fungal diseases which limits the production and productivity of the crop. The disease is caused by an obligate fungus, Peronosclerospora sorghi (Weston & Uppal) with varying symptoms. Information on the genetic diversity and population structure of P.sorghi in sorghum is imperative for the screening and selection for resistant genotypes and further monitoring possible mutant(s) of the pathogen. Isolates of P. sorghi infecting sorghum are difficult to discriminate when morphological descriptors are used. The use of molecular markers is efficient, and reliably precise for characterizing P. sorghi isolates. This study was undertaken to assess the level of genetic diversity and population structure that exist in P. sorghi isolates in Uganda. A total of 195 P. sorghi isolates, sampled from 13 different geographic populations from 10 different regions (agro-ecological zones) was used. Eleven (11) molecular markers, comprising of four Random amplified microsatellite (RAM) and seven (7) Inter-Simple Sequence Repeat (ISSR) markers were used in this study. The analysis of molecular variation (AMOVA) based on 11 microsatellite markers showed significant (P < 0.001) intra-population (88.9 %, PhiPT = 0.111) and inter-population (8.4 %, PhiPR = 0.083) genetic variation, while the genetic variation among regions (2.7 %, PhiRT = 0.022) was not significant. The highest genetic similarity value (0.987 = 98.7 %) was recorded between Pader and Lira populations and the lowest genetic similarity (0.913 = 91.3 %) was observed between Namutumba and Arua populations. The mean Nei's genetic diversity index (H) and Shannon Information Index (I) were 0.308 and 0.471 respectively. Seven distinct cluster groups were formed from the 195 P. sorghi isolates based on their genetic similarity. Mantel test revealed no association between genetic differentiation and geographical distance (R 2 = 0.0026, p = 0.02) within the 13 geographic populations.

New sources of sorghum resistant genotypes to downy mildew disease in Uganda

“…The mean yield recorded at MUARIK ranged between 0.92 t/ha (P 20) to 2.32 t/ha PI 656061 (QL3-India), whiles the mean yield at Abi-ZARDI ranged between 0.55 t/ha (E 2) to 1.91 t/ha PI 656061 (QL3-India). Since the same genotypes were evaluated at both locations, the observed significant difference can be attributed to the effect of downy mildew disease pressure (PDI and AUDPC values) and possible occurrence of P. sorghi pathotypes (Kumi et al 2018b). Low sorghum yield recorded at Abi-ZARDI was due to high disease pressure at the location compared to high yield in MUARIK and this finding corroborated to the linear association for downy mildew disease impact on yield decline/loss (Wall et al 1992).…”

Genetic diversity and population structure of Uganda’s yam (Dioscorea spp.) genetic resource based on DArTseq

“…Numerically coded data were subjected to AMOVA with 999 permutations. The genetic variations were partitioned into two: variation among the population (PhiPR) and variation within the population (PhiPT) [ 42 ]. Also, phylogenetic relationships among genotypes based on geographical origins were built using a Euclidean distance matrix in PowerMarker (v3.25) [ 33 ].…”