SEARCH FOR SOURCES OF EARLY BLIGHT (ALTERNARIA-SOLANI) FIELD-RESISTANCE NOT ASSOCIATED WITH VEGETATIVE LATE MATURITY IN TETRAPLOID POTATO GERMPLASM

A total of 934 potato cultivars and clones from different breeding pro grammes across the world were tested for their reaction to early bligh t (Altemaria solani) in Brasilia-DE Brazil. This field trial was set u p in order to identify tetraploid potato genotypes with useful levels of resistance to early blight (EB) that were not correlated with late maturity or lateness. Artificial inoculation (spread of A, solani infe cted leaves over plant canopy) was employed even though EB occurs natu rally at epidemic levels in the test area. Four disease assessments we re made every 10 days, beginning 45 days after planting. Based on the evaluation made 65 days after planting, only 27 clones were identified that had less lesioned leaf area than the resistant standard (cv. Ara cy). Area under disease progress curve (AUDPC) was also used as a crit erion of resistance. Using AUDPC as a parameter, 22 genotypes were ide ntified presenting values lower than or identical to cv. Aracy. Differ ences in the commercial yield were recorded in genotypes with identica l response to EB, suggesting that distinct levels of tolerance to EB a lso exist. In spite of the strong correlation between EB resistance an d late maturity, some genotypes derived from the parental materials 'N DD 277-2', 'Kufri Jyoti', 'CIP 377888-7', 'Maine-28', and the clones ' CFS 69.1' and 'I-853' were identified as having good levels of EB fiel d resistance not linked with the negative phenotypic trait of lateness . These materials presented medium to medium-early maturity with a veg etative cycle of around 90-95 days. Some selected genotypes presented more acceptable agronomic characteristics including resistance to Phyt ophthora infestans, potato leaf roll luteovirus (PLRV) and potato viru s Y (PVY). The EB resistance sources identified in this work can be re commended as parental materials for widening the genetic base for EB d isease resistance in breeding programmes for highland tropical and sub tropical areas.