Comparative Reliability of Screening Parameters for Anthracnose Resistance in Water Yam (Dioscorea alata)

Abstract

Anthracnose, caused by Colletotrichum gloeosporioides, is one of the major constraints limiting water yam (Dioscorea alata) production in the tropics. In this region, yam anthracnose control is mostly achieved by the deployment of moderately resistant yam genotypes. Therefore, screening for new sources of anthracnose resistance is an important aspect of yam research in the tropics. The reliability and applicability of different yam anthracnose rating parameters has not been fully examined. Disease severity on detached leaves in the laboratory and leaf severity, lesion size, and spore production on whole plants in the greenhouse were used to screen an F1 yam population and correlate screening results with field evaluations. Anthracnose lesion size had the smallest predicted residual means but whole-plant severity and detached-leaf severity had the best variance homogeneity and relatively small predicted residual means. The concordance correlation coefficient (rc) and κ statistic were used to determine the agreement between anthracnose rating parameters and field evaluations. Detached-leaf (rc = 0.95, κ = 0.81) and whole-plant (rc = 0.96, κ = 0.86) evaluations had high positive agreement with field evaluation but spore production (κ = 0.69) and lesion size (κ = 0.57) had moderate positive agreement. These results suggest that all the evaluated rating parameters can be used to successfully screen yam germplasm for anthracnose resistance but lesion size and spore production data may need to be transformed.

An EST-SSR based genetic linkage map and identification of QTLs for anthracnose disease resistance in water yam (Dioscorea alata L.)

“…A set of 41 C. gloeosporiodes isolates collected from five different countries in West Africa was studied for their differences in causing anthracnose on different D. alata varieties using detached leaf technique and whole-plant inoculation [14]. Eleven out of 41 isolates showed high virulence and a PCA graph was used to estimate their virulence based on the distance from the centre (Fig 1).…”

“…The highly virulent isolate Kog01R1 from Nigeria was selected to evaluate the mapping population consisting of the two parents and their ninety-four progenies. Kog01R1 has the features to exhibit high virulence at all stages of experiments carried out and it also showed the highest rate of infection in all the tested yam varieties, although there was variation in the rate of infection [14]. It is similar in characteristics to the fast-growing gray (FGG) isolates of C. gloeosporioides , and Abang et al [24] stated that FGG group is of high virulence as observed based on morphological characterization of isolates.…”

“…A mapping population of D. alata consisting of 94 progenies developed from a cross of two diploid genotypes including TDa 95-310 (susceptible male parent) and TDa 95/00328 (moderately resistant female parent) was used in the study. Both parents are breeding lines developed at IITA and showed differential reactions to several isolates of Colletotrichum gloeosporioides [14]. Tubers of 96 yam genotypes, including both parents, were sliced into minisetts of 20-25 g and planted in plastic pots filled with sterilized soil.…”

“…Recent studies focusing on biodiversity of C. gloeosporoides that associates with yam in the French West Indies [8, 9], in Nigeria [10, 4] and West Africa [11] revealed high genetic and pathogenic variance among the isolates. This high genetic and pathogenic variation in the populations of C. gloeosporiodes suggests that there is high likelihood for the breakdown of existing resistance and development of new strains of the pathogen [12, 13, 14]. Screening exotic germplasm accessions and selecting for new sources of durable disease resistance is the most reliable approach to long-term management of this disease.…”

“…Screening exotic germplasm accessions and selecting for new sources of durable disease resistance is the most reliable approach to long-term management of this disease. However, it is challenging to adequately evaluate yam genotypes for anthracnose disease response under multi-location field conditions because of the high variation among the pathogen isolates and variability in symptoms development across seasons [13, 14]. Furthermore, the standardization of screening protocol for anthracnose disease scoring is underway (Kumar et al, unpublished), although disease screening in controlled environments is favorable for both disease development and plant growth [15, 16].…”