ISHS Acta Horticulturae 470: II International Symposium on Pistachios and Almonds
ALMOND ANTHRACNOSE IN CALIFORNIA - A NEW PRE- AND POSTHARVEST FUNGAL DISEASE OUTBREAK |
| Authors: | J.E. Adaskaveg, H. Förster, R.J. Hartin, B. Teviotdale, J.H. Connell, R. Duncan |
| Abstract:
In the spring of 1995, a serious outbreak of almond anthracnose was observed in the Sacramento (Butte, Tehama, and Colusa Co.) and San Joaquin (Merced and Stanislaus Co.) valleys of California. The fungal pathogen was characterized and identified as Colletotrichum acutatum, rather than the previously reported C. gloeosporioides, using morphology, molecular techniques, and fungicide sensitivity assays. Using random and simple repeat primers, two distinct sub-populations could be identified among the isolates of C. acutatum that correlated with cultural pigmentation (pink vs. gray) and sensitivity to benomyl at low conidial concentrations. Butte, Carmel, Fritz, Harvey, Mission, Monterey, Peerless, Price, Thompson, and NePlus Ultra were the most commonly infected cultivars but the disease was also found on Nonpareil. The disease affected blossoms, leaves, fruit, and small branches of almond. Disease symptoms on young fruit included tan to orange, circular, and sunken lesions. Infections during later stages of fruit development often produced profuse gumming. Leaves attached to infected spurs often yellowed, wilted, and died but remained attached (similar to brown rot). Fruit symptoms were generally observed 2–3 weeks after petal fall and appeared like almond blanks (unfertilized fruit). Symptoms continued to appear until just before hull split. The fungus overwintered in mummified fruit. Recently, the organism also has been isolated from processed almond kernels in storage. Symptoms included brown and purplish discoloration of the kernel tissue. Percentage of quality assurance tests with positive samples of anthracnose-infected kernels was 0, 2, 10, and 10% for Nonpareil, Butte, Carmel, and Mission, respectively. Koch's postulates were performed in both laboratory and field inoculation studies demonstrating causality and pathogenicity of the almond-isolated Colletotrichum acutatum. Thus, the disease caused direct pre- and postharvest losses of the almond crop by infecting fruit and kernels, as well as indirect losses by causing shoot and branch dieback of trees. Fungicides evaluated | |
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