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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Publications at this Location » Publication #312792
Title: Diversity of Diaporthe species associated with wood cankers of fruit and nut crops in northern California

Author
item LAWRENCE, DANIEL - University Of California
item TRAVADON, RENAUD - University Of California
item Baumgartner, Kendra

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2015
Publication Date: 10/1/2015
Citation: Lawrence, D., Travadon, R., Baumgartner, K. 2015. Diversity of Diaporthe species associated with wood cankers of fruit and nut crops in northern California. Mycologia. 107(5):926-940. doi: 10.3852/14-353.

Interpretive Summary: Diaporthe ampelina, the fungus that causes the disease of grapevine leaves and fruit, ‘Phomopsis cane and leaf spot’, also causes a disease of the grapevine wood, ‘Phomopsis dieback’. In California, this and other Diaporthe species attack a range of tissues not only on grape, but also on other fruit and nut crops. To better understand the role of Diaporthe species in Phomopsis dieback of grapevine, and the potential for infection routes among alternate hosts, 76 Diaporthe isolates were recovered from wood cankers of grape, pear, apricot, almond, and the wild host willow in four California counties. Isolates were characterized based on their appearance while growing in petri plates and their genetic relationships. This study identified eight Diaporthe species associated with wood cankers of grapevine and one new species from willow, D. benedicti. We report the first findings of D. australafricana and D. novem in North America. Our findings also expand the host ranges of D. australafricana to almond and willow, D. ambigua to apricot and willow, D. novem to almond, D. foeniculina to willow, and D. chamaeropis to grapevine and willow. The generalists D. eres and D. ambigua were the most genetically-diverse species, based on two measures of genetic diversity, followed by the grapevine specialist D. ampelina. Our analysis of multilocus linkage disequilibrium provided evidence that D. ambigua reproduces sexually in nature, which is further supported also by our finding of relatively high haplotypic diversity, in addition to previous reports of the presence of both mating types and successful matings in vitro. Through inoculations of all of the species, D. ampelina was the most pathogenic species to grapevine wood, but the new species D. benedicti (isolated exclusively from willow trees) was also pathogenic.

Technical Abstract: Diaporthe ampelina, causal agent of Phomopsis cane and leaf spot of grapevine (Vitis vinifera L.), is also frequently isolated from grapevine wood, causing Phomopsis dieback. In California, Diaporthe species cause a wide range of symptoms not only on grape, but also other fruit and nut crops. To better understand the role of Diaporthe species in Phomopsis dieback of grapevine, and the potential for infection routes among alternate hosts, 76 Diaporthe isolates were recovered from wood cankers of grape, pear, apricot, almond, and the wild host willow in four California counties. Isolates were morphologically characterized and assigned to species based on multi-gene sequence analyses. This study identified eight Diaporthe species associated with wood cankers of grapevine and one novel taxon from willow, D. benedicti. We report the first findings of D. australafricana and D. novem in North America. Our findings also expand the host ranges of D. australafricana to almond and willow, D. ambigua to apricot and willow, D. novem to almond, D. foeniculina to willow, and D. chamaeropis to grapevine and willow. The generalists D. eres and D. ambigua were the most genetically-diverse species, based on high nucleotide and haplotypic diversity, followed by the grapevine specialist D. ampelina. Analyses based on multilocus linkage disequilibrium could not reject the hypothesis of random mating for D. ambigua, which is further supported by relatively high haplotypic diversity, reports of both mating types, and previous reports of successful matings in vitro. Pathogenicity assays revealed that D. ampelina was the most pathogenic species to grapevine wood.