Charcoal Rot Resistance in Soybean: Current Understanding and Future Perspectives

Soybean (Glycine max L.) is a leading oil seed crop in the world. Owing to climate change, its production is challenged by many forms of biotic and abiotic stresses. Charcoal rot (Macrophomina phaseolina (Tassi) Goid) disease incidence is aggravated with the increase in soil and air temperatures. Charcoal rot disease in soybean is likely to gain its economic importance with the increase in global temperature. Apart from soybean, this pathogen has a wide host range including some economical crops like sorghum and maize. So far, complete resistance to this pathogen has not been identified in any of the crop species. Field screening techniques based on the colony-forming unit index (CFUI) and estimation of root stem severity (RSS) and glasshouse screening technique, such as cut-stem inoculation, are mainly employed in identifying charcoal rot resistance sources in soybean. High-throughput screening can be possible through cut-stem inoculation technique. There are reports indicating the correlation between field screening results and results obtained from this technique, and researchers have used this technique in understanding the genetic architecture of charcoal rot resistance and in identifying candidate genes and QTL governing charcoal rot resistance. Drought conditions are favourable for disease incidence and aggressiveness. Not all drought-tolerant genotypes are resistant to charcoal rot but some drought-tolerant genotypes are found to be moderately resistant to the disease. Significant yield losses are reported due to this disease even under irrigated conditions. Research is gaining momentum in developing high-throughput, reliable and repeatable glasshouse and in vitro screening techniques to identify stable sources of resistance and in understanding the genetic architecture of charcoal rot resistance. Breeding programs are under way for developing high-yielding, charcoal-rot-resistant and drought-tolerant cultivars.