New sources of resistance to Sclerotinia stem rot caused by Sclerotinia sclerotiorum in Chinese and Australian Brassica napus and B-juncea germplasm screened under Western Australian conditions

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a serious problem in oilseed rape in China and Australia. Locating effective sources of host resistance offers the best long-term prospects for improved management of this disease. For these reasons, 93 genotypes of Brassica napus and B. juncea from China and Australia were screened in the field for resistance to S. sclerotiorum under semi-field conditions in Western Australia using a stem inoculation test. There were significant differences (P < 0.001) among genotypes in relation to the severity of the disease measured as stem lesion length. Among the B. napus genotypes, ZY006 showed outstanding resistance, with a mean stem lesion length of <0.45 cm, a level of resistance far superior to that ever identified previously in Australia for B. napus or B. juncea. B. napus genotypes 06-6-3792 and ZY004 from China and RT108 from Australia showed very high levels of resistance, with mean stem lesion lengths <3 cm. The most resistant B. juncea genotypes were JM06018 and JM06006 from Australia and B. juncea 2 from China with mean stem lesion lengths of <= 4.8 cm. The outstanding resistance to S. sclerotiorum identified in B. napus ZY006 provides the first such level of resistance available for oilseed Brassica breeding programs in Australia.