Response of Sorghum Accessions against Newly Documented Pathotypes 5 and 6 of Head Smut Pathogen, <i>Sporisorium reilianum</i>

This study was conducted to identify resistance sources against the newly documented pathotypes (P5 and P6) of Sporisorium reilianum, causing sorghum head smut. A subset of 67 sorghum association panel (SAP) accessions, 29 in 2017 and 38 in 2018 along with checks BTx635 (resistant) and BTx643 (susceptible) were screened in the greenhouse against P5 and P6 pathotypes in two separate experiments in both years. At 18 to 20 days after planting, accessions were inoculated by injecting the seedlings below the apical meristem with sporidial suspensions following an established inoculation procedure. Three accessions (PI656091, PI533919, and PI533821) in 2017 and 17 accessions (PI597961, PI656071, PI656048, PI576435, PI534075, PI534145, PI656057, PI576437, PI651492, PI656014, PI656025, PI655999, PI656010, PI656082, PI534123, PI533927, PI656100) in 2018 were identified as potential resistant sources to both P5 and P6 pathotypes of S. reilianum. These SAP accessions are new sources that can be further used to develop new breeding parental lines and hybrids and mapping populations for quantitative trait loci markers closely linked to head smut resistance.

Response of Sorghum Accessions from Four African Countries against <i>Colletotrichum sublineolum</i>, Causal Agent of Sorghum Anthracnose

Seventy-two sorghum accessions were randomly selected from the Ethiopia, Mali, Sudan, and Uganda germplasm collections maintained by the US National Plant Germplasm System to evaluate variation in anthracnose resistance. The accessions were planted in a randomized complete block design in College Station, Texas during the 2007 and 2008 growing seasons. Twenty-six accessions exhibited a resistant response across growing seasons with 8 accessions showing a susceptible response. Twenty-nine accessions showed variation in disease response within and between experiments. Seven accessions were rated as resistant in 2007 but showed a susceptible reaction in 2008. The frequency of resistant germplasm varied based on country of origin with 80% of the accessions from Mali, 48% of the accessions from Uganda, 24% of the accessions from Sudan, and 7% of the accessions from Ethiopia exhibiting a resistance response. When the same accessions were evaluated in Isabela, Puerto Rico, 100% of the accessions from Mali, 43% of the accessions from Uganda, and 28% of the accessions from Sudan exhibited a resistant response. All the accessions from Ethiopia were susceptible to anthracnose when evaluated in Isabela, Puerto Rico. In both locations, 22 accessions exhibited a resistant response. Four accessions rated as resistant in Texas were found to be susceptible in Puerto Rico;whereas, five accessions rated as resistant in Puerto Rico showed a susceptible response in Texas. These results indicated that the Mali, Sudan, and Uganda sorghum collections may be an important source of anthracnose resistance. However, the identification of anthracnose resistant germplasm from many diverse regions could result in the identification of new sources of genetic variation for resistance. Also, greater genetic variation for resistance could be present in regions with a high frequency of resistant germplasm.