Study on susceptibility of longan cultivars to longan witches' broom syndrome in Vietnam

Study on susceptibility of selected and hybrid longan cultivars to longan witches’ broom syndrome (LWB) was conducted at the Plant Protection Division of the Southern Horticultural Research Institute (SOFRI), Vietnam from January 2016 to December 2018. Eighteen cultivars, 13 hybrid clones and seven mutants were tested for their resistance to LWB using a mite inoculation method. Data were recorded every two weeks. Observed parameters were LWB incidence, in which the damage level caused by LWB was determined (scored) as per methods described by Croxall et al. (1952), Mustafa et al. (2014, 215), and Grassroot Standards of SOFRI (2017). Results showed that among 18 selected cultivars, 9 cultivars such as ‘Long’, ‘Super’, ‘Soc Trang’, ‘Bay To’, ‘Xuong Com Vang-Tien Giang’, ‘Xuong Com Vang-XCVBR30’, ‘Xuong Com Vang-XCVBR33’, ‘Xuong Com Rao-XCRBR12’ and ‘Xuong Com Rao-XCRBR18’ showed tolerance against LWB with infection rating of 1. For the 13 hybrid clones tested for susceptibility against LWB, hybrid clones of ‘T-87’, ‘T-160’, ‘X-138’ and ‘09NL-081’ showed tolerance against LWB with infection rating of 1. The hybrid clone ‘LD11’ showed moderate tolerance against LWB with infection rating of 3. ‘T-06’ and ‘T-208’ showed moderately susceptible response against LWB with infection rating of 5. The hybrid clones of ‘NL-19’, ‘T-01’ and ‘T-140’ were susceptible with infection rating of 7. The hybrid clones of ‘T-03’, ‘T-207’ and ‘X-148’ were highly susceptible with infection rating of 9. Seven mutants, ‘TH 1.1-1’, ‘TH 1.1-34’, ‘TH 1.1-39’, ‘TH 1.1-44’, ‘TH1.1-76’, ‘TH 1.1-204’ and ‘TH 1.2-541’, showed tolerance against LWB.