Evaluation of Disease Resistance of the Cassava Lines Introduced from Nigeria to Sri Lankan cassava mosaic virus, the Causal agent of Cassava Mosaic Disease

Abstract

The first outbreak of cassava mosaic disease (CMD) in Thailand was reported in 2019. The causal virus was Sri Lankan cassava mosaic virus (SLCMV). The disease destructive cassava tuber yield losses due to the introduction of the infected cutting cassava for planting across the country. To control CMD, we seek CMD-resistant cassava lines as a resistant source in plant breeding. In this research, five cassava lines resistant to CMD were introduced from Nigeria and evaluated for resistance to SLCMV under greenhouse conditions. Artificial inoculation was performed by top grafting the virus-free Nigerian cassava lines onto the SLCMV-infected shoots of CMR43-08-89, a susceptible cassava line. Disease severity and incidence were recorded 2-8 weeks after inoculation (WAI). The results revealed that all five Nigeria cassava lines, including IITA-TMS-IBA 980581, IITA-TMS-IBA 972205, IITA-TMS-IBA 980505, IITA-TMS-IBA 920057 and TME B419 were susceptible to SLCMV with 100% disease incidence. All grafted plants showed positive detection of the virus by PCR. The mean severity score of the infected cassava lines was 2.11-2.56. The control line C33 was resistant (R), while TME3 was susceptible (S). The detection of the SLCMV in both symptomatic and asymptomatic young leaves of all tested cassava lines indicated the tolerance reaction of some cassava lines.