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 programmes across the world were tested for their reaction to early blight (Altemaria solani) in Brasilia-DE Brazil. This field trial was set up 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 infected leaves over plant canopy) was employed even though EB occurs naturally at epidemic levels in the test area. Four disease assessments were 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. Aracy). Area under disease progress curve (AUDPC) was also used as a criterion of resistance. Using AUDPC as a parameter, 22 genotypes were identified presenting values lower than or identical to cv. Aracy. Differences in the commercial yield were recorded in genotypes with identical response to EB, suggesting that distinct levels of tolerance to EB also exist. In spite of the strong correlation between EB resistance and late maturity, some genotypes derived from the parental materials 'NDD 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 field resistance not linked with the negative phenotypic trait of lateness. These materials presented medium to medium-early maturity with a vegetative cycle of around 90-95 days. Some selected genotypes presented more acceptable agronomic characteristics including resistance to Phytophthora infestans, potato leaf roll luteovirus (PLRV) and potato virus Y (PVY). The EB resistance sources identified in this work can be recommended as parental materials for widening the genetic base for EB disease resistance in breeding programmes for highland tropical and subtropical areas.