Progress in Breeding Peanut for Resistance to Leaf Spot Diseases.

Breeding peanut for resistance to leaf spot diseases (Early leaf spot [Cercospora arachidicola S. Hori] and Late leaf spot [Cercosporidium personatum (Berk and M. A.Curtis)) has been a goal of the University of Florida peanut breeding program for over 30 years.   Moderate resistance was identified in PI203396 and related lines in the early 1970’s.  Using PI203396, six cultivars with moderate resistance to leaf spot have been developed by the University of Florida since 1986.  However, only one of these cultivars was commercially successful.  The other five suffered from poor seed germination and/ or poor seedling vigor and commercial production was terminated as a result.   In addition to their resistance to leaf spot, these lines share common characteristics such as late relative maturity and resistance to spotted wilt and white mold diseases.  Growers would benefit from this combination of traits so there is a need to understand why this group of germplasm suffers from poor seed germination.   On-going research to determine the cause of poor seed germination and/or poor seedling vigor has identified several factors.  First, the seed storage environment was found to reduce the germination and vigor of seeds of DP-1 but not other cultivars.  Second, seeds of DP-1 were found to contain less calcium than other cultivars.  In peanut, insufficient seed calcium concentration is linked to poor seed germination.  Subsequently, seeds of several other lines and cultivars with characteristics and genetic background similar to DP-1 were found to have lower seed calcium concentration than other cultivars.  Third, electrolyte leakage of seeds of DP-1 was greater than other cultivars and was correlated with germination and seedling emergence.   Preliminary data suggests that the antioxidant capacity of DP-1 is less than other cultivars which could explain greater electrolyte leakage.  This report will summarize the status of research in these areas.