ARET, Annual Report 2001, p. 119-21.

Screening of tobacco cultivars for resistance to potato virus Y disease in Malawi

ANON.
ARET, Agricultural Research and Extension Trust, Lilongwe, Malawi
Potato Virus Y (PVY) disease of tobacco is becoming a problem in Malawi. Some estates in Zomba, Machinga and Thyolo were seriously affected (25-50% infection) in 1999/2000 and 2000/2001 seasons. The disease occurs worldwide and is of great economic importance. It also affects Irish potato, pepper, and tomato and weed species e.g. Solanum nigrum, Portulaca olearacea, Senecio vulgaris and Physalis spp and causes severe losses in all these hosts. This diversity in host range helps assure, among other things, the preservation of PVY pathogen during the winter months. The disease becomes serious in tobacco producing areas where potatoes are an important crop. The best method to contr al PVY is to use resistant varieties. The objective of this trial, which was run in collaboration wiht CORESTA was to identify sources of PVY resistance. The trial was conducted Msamba, Makoka and Kachulu in the Southern Region and at Msunga in the Central Region where natural disease pressure was high and no artificial inoculation would be required. The test varieties were: nine from CORESTA (Burley 21, MN944, K326, NC95, Virginia SCR, TN86, PBD6, VAM, NCTG52) and eight from Malawi (Banket A1 Zimbabwe, KBM33, MTRA 88, MW86-57, ABL 34, ABL 109, FLS 89-109, FLS89-90) in a randomised complete block design with three replications. Although the season was favourable for disease development, the severity of the disease was lower than expected at Kachulu and Makoka but high at Msamba Estate. At this site, the disease was most severe because the trial was cited near a forest, which could have had some alternate hosts and both mosaic and necrotic symptoms were observed. Based on the reaction of the varieties at this site, MW86-57, KBM 20, BW94/6/5, PBD6 and ABL 109 showed high resistance to the varieties and VAM showed no symptoms. The disease pressure was high at Msamba and low at the other sites. The selection of resistant varieties was therefore based on the reaction to the disease only at Msamba. At this site, Kachulu, and Makoka where the disease was noticed, both necrotic and mosaic symptoms were observed. The seven varieties which showed high resistance to the disease, were VAM, PBD 6, ABL 109, MTRA 88, KBM 2, BW94/6/5 and KBM 20. These results indicate the potential in the local cultivars that can be used for breeding for resistant varieties to PVY.