HAZELNUT KERNEL MOLD IDENTIFICATION AND TIMING OF INFESTATION

Fungal organisms were isolated during hazelnut kernel development to try to identify a type of white mold on the kernels at harvest. It was found that Ramularia spp. was present from the very earliest stages of nut development, and was the major pathogen associated with kernel tip mold. This weak pathogen seems to be associated with the microclimate of the funiculus attachment to the embryo portion of the developing kernel. Other orchard factors, including varietal differences, are discussed which may infleunce the fungus. While other fungi, including some types of Aspergillus spp., there was no evidence of any known aflatoxin-producing species. Once the kernels are properly dried, neither the disease incidence nor the severity increase, unless the nuts are held under high humidity conditions favoring resumption of mold growth.

In the Pacific Northwest we have a type of kernel mold which has not been previously identified, and the incidence of this problem is about 5% annually, but may be considerably more under early spring wet climate conditions. The characteristics of the mold is that it is almost always located at the attachment point of the funiculus to the tip of the kernel. The objectives of this study were to identify the mold(s), identify time of infection during nut development, and characterize varietal susceptibilities, and other orchard factors affecting the disease.

Mold colonies were isolated from diseased kernels at harvest and were taxonomically categorized at genus and, if possible, Bat the species level. By far the most common organism associated with the tip mold of hazelnut kernels was Ramularia spp. And even though other fungi were present, Ramularia was always associated with the tip mold. Although wè did not begin to sample at hazelnut time of bloom, we did sample as soon as developing fruits were evident, about 4 mm in size, and Ramularia spores were already present, and was present throughout nut development. Interestingly, all species of fungi, including Ramularia, decreased as nuts developed to maturity. Despite the presence of live Ramularia isolates within the hazelnut shell, only a small percentage of kernels actually became sufficiently infected to present disease symptoms.

Although there were some consistent hazelnut varietal differences in susceptibility to the pathogen, and differences from one season to another were observed (largely attributable to climatic differences), other factors such as age of trees, location in the canopy, numbers of nuts per cluster, and or whether the nuts dropped early or late seemed to have little effect on the incidence of the disease.

Thus, even though Koch's postulates (such as isolation of the organism and proof of reinfection) have not been firmly established in this case, the most likely candidate organism associated with kernel tip mold appears to be Ramularia spp.