Marcelo I. Bustamante

Avocado (Persea americana Mill.) production in Peru is economically impacted by stem-end rot (SER) and branch canker (BC). Although Lasiodiplodia species are recognized pathogens of BC, the etiology of SER remains understudied. From 2018 to 2022, healthy-looking fruits and symptomatic branches were collected from twelve ‘Hass’ groves across seven Peruvian regions. Lasiodiplodia spp. were frequently isolated, detected in 86.4% of SER samples and 95.4% of BC samples. Morphological and multilocus phylogenetic analyses identified L. theobromae (n = 374), L. pseudotheobromae (n = 113), L. laeliocattleyae (n = 42), L. brasiliensis (n = 4), Lasiodiplodia sp. (n = 1), and L. euphorbiaceicola (n = 1). Koch’s postulates were fulfilled for all six species on inoculated Hass fruits using isolates obtained from SER and BC samples, with controls remaining symptomless. Pathogenicity was also confirmed for five species recovered from BC samples on stems of 1-year-old trees. Aggressiveness varied significantly among isolates, suggesting isolate-specific virulence. This study represents the first report of L. theobromae, L. pseudotheobromae, L. laeliocattleyae, L. brasiliensis, and L. euphorbiaceicola as causal agents of SER, and of L. brasiliensis and Lasiodiplodia sp. associated with BC of avocado in Peru. These findings provide novel insights into the diversity and pathogenicity of Lasiodiplodia species affecting avocado and highlight the importance of species-level identification to guide disease management.

Anthracnose, caused by Colletotrichum species, is a major disease of avocado (Persea americana) that significantly reduces fruit quality and export potential in Chile. Colletotrichum species associated with this disease were identified and their pathogenicity to avocado was assessed. In the summer of 2018, healthy fruits (n = 1,335) were sampled from three commercial groves located in the Metropolitan, O’Higgins and Valparaíso regions of Chile, and from a non-commercial grove and local markets. Fruits were stored until symptoms developed, indicating anthracnose incidence in commercial groves ranging from 10 to 50%. A total of 146 fungal isolates were obtained from symptomatic fruit and were initially identified as Colletotrichum spp. Fifty representative isolates were further identified through multilocus phylogenetic analyses. Ten species belonging to four species complexes were identified. Colletotrichum cf. cigarro was the most frequent taxon (n = 17), followed by C. pyricola (n = 9), C. gloeosporioides (n = 6), C. jiangxiense (n = 5), C. karsti (n = 4), C. anthrisci (n = 3), C. brassicicola (n = 3), C. laurosilvaticum (n = 1), C. fructicola (n = 1), and C. perseae (n = 1). Pathogenicity tests reproduced anthracnose symptoms in inoculated fruits, whereas control fruits remained symptomless, and revealed differences in virulence among isolates and species. This study provides the first report of C. brassicicola, C. laurosilvaticum and C. pyricola as causal agents of avocado anthracnose, highlights the diversity of Colletotrichum species in Chilean avocado groves, and provides insights for improved management strategies for avocado anthracnose.

Summer bunch rot (SBR) is a late-season grape disease complex caused primarily by Botrytis cinerea, with secondary colonizers including Alternaria, Aspergillus, Cladosporium, Penicillium, and Rhizopus species. Symptoms develop after berry ripening and increase in severity when berries are injured. Affected clusters exhibit berry decay, shriveling, and juice leakage, which attract vinegar flies and may lead to sour rot development. Masses of black, brown, or green spores form on the surface of decayed berries, providing visual signs of the fungal groups present. This report evaluates the efficacy of fungicide programs consisting of experimental and registered biological and synthetic products for SBR management in California. The trial was conducted in 2025 in Clarksburg, CA, in a mature 13-year-old Riesling vineyard. The outcomes of this research provide practical guidance for U.S. grape growers in optimizing disease management strategies under regional production conditions.

Botryosphaeria dieback, caused by species in the Botryosphaeriaceae family, is a major grapevine trunk disease worldwide. Symptoms include vine decline, spurs and cordons dieback, and wedge-shaped wood necrosis. Infection occurs through pruning wounds, which remain susceptible for weeks. Therefore, wound protection is key to integrated management. This study evaluated efficacy and persistence of registered fungicides and a biological protectant against host-jumping Botryosphaeriaceae isolates. Field trials were conducted in 2024 on Vitis vinifera cultivar Cabernet Sauvignon in the Maule, Chile. Results showed that infection levels ranged from 6.7 to 26.7% for treatments applied 1 day after pruning and from 33.3 to 53.3% for treatments applied 15 days postpruning, highlighting the importance of timely application for optimal disease control. These findings provide evidence to guide grower decisions on pruning wound protection to reduce dieback risk.

Grape powdery mildew, caused by Erysiphe necator, is one of the most economically important grape diseases worldwide, significantly reducing crop yield and quality. All green tissues of the vine are susceptible to infection; therefore, intensive fungicide applications are implemented throughout the growing season. Symptoms first appear as chlorotic spots on the upper surface of leaves accompanied by white to grey mycelium with a filamentous aspect on the lower surface. On fruit and rachises, infections produce white, powdery masses that can cover the entire cluster surface, reducing photosynthesis and causing berry cracking. This report evaluates the efficacy of fungicide programs for the management of powdery mildew in table grapes in Kern County, CA. The trial was conducted in 2024 in a 6-year-old Vitis vinifera ‘Flame Seedless’ vineyard. Results from this trial provide valuable insights for U.S. grape growers in optimizing fungicide application timing and coordination to enhance disease management.

Apricot (Prunus armeniaca L.) is an important and widely grown fruit crop in Türkiye. In the last 15 years, symptoms of branch dieback and gummosis have been observed in commercial apricot orchards. A survey conducted in 2015 across 44 apricot orchards in the Adana and Mersin provinces revealed consistent infections caused by Botryosphaeriaceae fungi. From symptomatic branch samples (n = 232), a total of 128 fungal isolates with botryosphaeriaceous morphology were recovered, representing an incidence of 55.2%. Preliminary morphological identifications suggested the presence of three species. Representative isolates from each morphological group were identified as Diplodia seriata (n = 10), Neofusicoccum parvum (n = 7), and Lasiodiplodia mediterranea (n = 1), based on phylogenetic analyses of nucleotide sequences from the ribosomal DNA internal transcribed spacer, beta-tubulin and translation elongation factor 1-alpha genes. Mycelium growth rates were different among the three species, and the optimal growth temperatures were estimated as 26.2°C for D. seriata, 27.4°C for N. parvum, and 28.9°C for L. mediterranea. Pathogenicity of the identified fungi was confirmed on 2-year-old ‘Tyrinthe’ apricot seedlings, with L. mediterranea being the most virulent, followed by D. seriata, and N. parvum. This is the first report of D. seriata, N. parvum, and L. mediterranea causing branch dieback and gummosis of apricot in Türkiye.

Pine ghost canker is a recently described disease affecting multiple pine species in urban forests of Southern California. Symptoms include wedged cankers with irregular margins and cryptic discoloration on cross sections of branches, which can lead to severe dieback and potentially tree death. In this study, we identified and characterized five Neofusicoccum species (N. luteum, N. mediterraneum, N. parvum, N. stellenboschianum, and N. vitifusiforme) as the primary etiological agents of pine ghost canker. These pathogens were consistently isolated from multiple symptomatic pine samples (n = 41) and identified by morphology and phylogenetic analyses using four DNA barcodes (rDNA ITS, tef1, tub2, and rpb2). Pathogenicity was confirmed on healthy branches of 15-year-old Monterey pines, where the five Neofusicoccum species caused vascular lesions that were not significantly different in length. Secondary fungi (Diaporthe, Diplodia, Neopestalotiopsis, and Pestalotiopsis spp.) were also recovered from symptomatic tissues but did not cause vascular lesions in pathogenicity tests. The five Neofusicoccum species showed significant differences in mycelial growth rate at 20, 25, and 30°C. The optimal temperature for mycelial growth of N. luteum and N. parvum was 30°C, whereas for N. mediterraneum, N. stellenboschianum, and N. vitifusiforme, it was 25°C. All five species were able to resume growth at 20°C after showing no growth during a 7-day exposure to 5 and 40°C. This study also constitutes the first report of N. luteum, N. stellenboschianum, and N. vitifusiforme causing pine ghost canker in California. Environmental factors such as warmer temperatures, irrigation, and pest infestations are discussed as drivers of disease expression in pine trees. Management practices are also proposed.

Grape powdery mildew is a polycyclic disease caused by Erysiphe necator that reduces both crop quality and yield. It is considered one of the most economically important grape diseases worldwide. All green tissues of the vine are susceptible to infection if management strategies are not properly implemented. Initial symptoms appear on leaves as chlorotic spots on the upper surface. Shortly thereafter, signs of the pathogen emerge as a white to grey, web-like mycelium on the lower leaf surface. On fruit and rachises, the pathogen develops as white, powdery masses that may colonize the entire cluster surface. This report evaluates the efficacy of experimental and registered biological and conventional fungicide programs for the management of powdery mildew in grapes. The trial was conducted in 2024 in Davis, CA, in a 13-year-old Vitis vinifera ‘Chenin Blanc’ vineyard. Results from these trials will inform U.S. grape growers in developing effective management programs for this disease.

Summer bunch rot, caused by multiple fungal pathogens such as Botrytis cinerea, Aspergillus spp., Rhizopus spp., Alternaria spp., Cladosporium spp., and Penicillium spp., is an economically important disease that affects grapes ( Vitis vinifera), especially in warmer areas of the San Joaquin Valley in California. Symptoms and signs include masses of black, brown, or green spores on the surface of the berries; leakage of berry juice; hairline cracks in the berry skin; watery discoloration of berries; general berry breakdown; and the presence of vinegar flies. This report evaluates the efficacy of experimental and registered biological and conventional fungicide programs for the management of summer bunch rot on grapes. The trial was conducted in 2023 in Clarksburg, CA, on an 11-year-old ‘Riesling’ vineyard. Results from this trial will help advise U.S. grape growers in improving management programs for this disease.

Powdery mildew is caused by Erysiphe necator; this polycyclic disease of grape causes reductions in crop quality and yield and is considered one of the most economically important diseases of grapes worldwide. All green tissues of the vine are susceptible and may be infected if management strategies are not properly applied. Initial symptoms of powdery mildew appear on leaves as chlorotic spots on the upper leaf surface. Signs of the pathogen appear shortly as a white to grey webby mycelium on the lower leaf surface. On fruit and rachises, the pathogen appears as white powdery masses that may colonize the entire cluster surface. This report evaluates the efficacy of experimental and registered biological and conventional fungicide programs for the management of powdery mildew on grapes. The trial was conducted in 2023 in Davis, CA, on a 12-yr-old Vitis vinifera ‘Chenin Blanc’ vineyard. Results from these trials will help advise U.S. grape growers in improving management programs for this disease.