Eastern black walnut (Juglans nigra) is a large tree endemic to the eastern United States and is highly sought after for its timber products and uniquely flavored nuts. The University of Missouri Center for Agroforestry in New Franklin, MO, USA, hosts an eastern black walnut cultivar repository. This collection supports an ongoing breeding program to improve economic performance for nut production (kernel weight, nut quality, precocity, and yield). In 1996, 54 cultivars were grafted and planted in a series of experimental orchards for evaluation. From 2001 until 2015, trees were evaluated for 12 phenological and eight nut quality/yield traits. Economically relevant traits including kernel weight, kernel percentage, and precocity (total nuts produced age 6 to 10 years) ranged from 1.1 to 8.6 g, 5.3% to 39.3%, and 16 to 1522 total nuts per tree, respectively. Kernel percentage was positively correlated with kernel weight (r = 0.51) and precocity (r = 0.38). Precocity was negatively correlated with the first (r = −0.39) and last (r = −0.30) female bloom. Principal component analysis and biplot analyses revealed high levels of variation among the cultivars. The first two components explain 43.4% of the total variation. Nut dimensions (nut length and nut thickness), nut and kernel weight, and kernel percentage are the largest drivers of variation in the collection. Eigenvectors for precocity and kernel percentage load together and are orthogonal to kernel weight, suggesting these three important traits can be improved simultaneously. Also, nut length loads with kernel weight, providing a candidate indirect selection parameter to increase kernel weight. These data inform strategies for crossing scheme design, expectations for multitrait genetic gain, complementary hybridization, and identifying unique recombinants.
U.S. chestnut (Castanea sp.) production is expanding as knowledge of seedling cultivation and germplasm advances. Chestnuts have high starch and water content, making them highly perishable; therefore, they require cold storage immediately following harvest. Postharvest spoilage remains a significant area for improvement. Several postharvest fungi (including Fusarium sp. and Penicillium sp.) can infect chestnuts during storage, leading to spoilage and nonsellable nuts. The annual crop losses can reach up to 10%, thereby affecting trees differently. Our research objectives were to 1) evaluate spoilage incidence on the interior (i.e., pellicle, kernel) and exterior (i.e., nutshell) of the nut over the course of 200 days of cold storage on eight cultivars and 2) assess the impact of food contact-approved chlorine solution and 2% peracetic acid (PAA) with 27% hydrogen peroxide prestorage treatments for spoilage suppression on ‘Qing’ nuts. Fourteen timepoints were observed during the study period, each with four replications of 16 nuts. An additional four replicates of 16 ‘Qing’ nuts were treated prestorage and observed over seven time points. The incidence of spoilage was reported as the percentage of nonsellable nuts for each treatment and cultivar at four timepoints. The nut interior showed the highest spoilage incidence after 200 days, with four cultivars having >30% nonsellable nuts. Overall, the cultivars had an average of 10% nonsellable nuts from interior spoilage after 60 days in storage. ‘Hong Kong’ had the highest percentage of nonsellable nuts by the end of the study at 60%, whereas ‘Qing’ and ‘Mossbarger’ had the lowest rates, with only 14% nonsellable nuts. Spoilage of the exterior, although less frequent, is visible to buyers and impacts nut marketability. ‘Kohr’ had the highest percentage of nonsellable nuts because of exterior spoilage (35.9%). ‘Mossbarger’ had the lowest percentage of nonsellable nuts because of exterior spoilage (3.1%). ‘Qing’ nuts treated with 500 ppm chlorine and 100/200 ppm PAA demonstrated reduced exterior spoilage with longer storage times. Prestorage treatment did not show efficacy for reducing interior spoilage. This study provides a preliminary report of evidence that cultivar differences influence the spoilage incidence and supports taking nuts to market within 60 days of harvesting. These preliminary data also inform breeding parent combinations and studies of inheritance for postharvest spoilage tolerance at the University of Missouri Center for Agroforestry breeding program.
The Chinese chestnut (Castanea mollissima Blume) and other Castanea species (Castanea spp. Mill.) have been imported and circulated among growers and scientists in the United States for more than a century. Initially, importations of C. mollissima after 1914 were motivated by efforts to restore the American chestnut [Castanea dentata (Marsh.) Borkh.], with interests in timber-type characters and chestnut blight resistance. Chestnut for orchard nut production spun off from these early works. Starting in the early 20th century, open-pollinated seeds from seedlings of Chinese chestnut and other Castanea species were distributed widely to interested growers throughout much of the eastern United States to plant and evaluate. Germplasm curation and sharing increased quite robustly through grower networks over the 20th century and continues today. More than 100 cultivars have been named in the United States, although a smaller subset remains relevant for commercial production and breeding. The University of Missouri Center for Agroforestry curates and maintains a repository of more than 60 cultivars, and open-pollinated seed from this collection has been provided to growers since 2008. Currently, more than 1000 farms cultivate seedlings or grafted trees of the cultivars in this collection, and interest in participatory on-farm research is high. Here, we report descriptions of 57 of the collection’s cultivars as a comprehensive, readily accessible resource to support continued participatory research.