Pistachio (Pistacia vera L.) progeny from the California cultivar improvement program were evaluated at two locations for their resistance to alternaria late blight [Alternaria alternata (Fries) Keissler] from 1995 to 1997. Large differences between seedlings were observed for disease resistance. Narrow sense heritabilities were calculated from half-sib analysis of 20 open pollinated families. Heritabilities of 0.48 and 0.11 at Kearney Agricultural Center were observed in 1995 and 1997, respectively. Narrow-sense heritability estimates were 0.56 and 0.54 at the Wolfskill Experimental Orchard near Davis for 1995 and 1997, respectively. Differences among progeny families to alternaria late blight infection were highly significant and were associated with the female parents. Greenhouse inoculation experiments were not strongly correlated with field results. Fifty-eight highly resistant seedlings were identified for use in future cultivar improvement efforts.
Alternaria late blight of pistachio caused by Alternaria alternata, has become a serious problem in pistachio orchards in California. As part of the California pistachio improvement program, we evaluated the resistance/susceptibility of the breeding progenies to Alternaria late blight at two locations. The heritability of resistance ranged from 0.35 to 0.38 based on half-sib progenies analysis. Open-pollinated (OP) progenies from three cultivars showed moderate to high resistance. Greenhouse inoculation confirmed that OP progenies of cultivars Bronte and Trabonella had the greatest resistance. OP progenies of cultivar Red Aleppo were highly susceptible in greenhouse inoculations compared to moderate resistance found in field evaluations. OP progenies of the only commercial cultivar Kerman in California were susceptible in both field and greenhouse evaluation. The results show the potential for development of resistant cultivars is available in the breeding population of the California pistachio improvement program.