First Report of Botryosphaeria dothidea Basal Canker of Pistachio Trees in South Africa

Effect of Photo-Selective Shade Nets on Pollination Process and Nut Development of Corylus avellana L

Hazelnut (Corylus avellana L.) is one of the most appreciated nut crops, which is motivating the cultivation outside its historical production areas. Despite that, there is still limited knowledge about the floral biology of the species and its developmental fruiting stages under different environments. Adverse climatic conditions can threaten the pollination process and fruit development. In South Africa, the deciduous fruit industry identified the net shading as a tool to mitigate the effects of unfavorable abiotic events. The objective of this work was to investigate the effects of photo-selective nets on the pollination process and nut development of C. avellana. Mature hazelnut trees were maintained under netting and compared with the ones in open field. Microscopic examination of female flower and developing nuts were conducted in order to observe the pollen tube growth and the pattern of disodium fluorescein transport into the funiculus and ovule. The results showed differences in pollen tubes growth and timing between the treatments. Generally, trees under nets showed higher rate in pollen tubes developing and reaching the base of the style. On the contrary, the tests carried out in open field showed a higher ratio of pollen tubes arrested in the style. The results also indicated differences in ovules abortion. Developing fruits that showed an interruption point at the funicle level or at junction point of the ovule were classified as aborting fruits (blank nuts at harvest time). A higher rate of abortion was detected in open field compared to the plants under netting. In conclusion, the shade nets influenced the pollen tube growth and the nut development, principally due to micro-climate modification. Therefore, further investigations are needed to analyze the influence of light spectra and to determine the sustainability of photo-selective nets over several years.

Identification and Pathogenicity of Fungal Species Associated with Canker Diseases of Pistachio in California

A survey was conducted during 2015 and 2016 in pistachio orchards throughout the San Joaquin Valley of California to investigate the occurrence of canker diseases and identify the pathogens involved. Cankers and dieback symptoms were observed mainly in orchards aged >15 years. Symptoms of canker diseases included brown to dark brown discoloration of vascular tissues, wood necrosis, and branch dieback. In total, 58 fungal isolates were obtained from cankers and identified based on multilocus phylogenetic analyses (internal transcribed spacer, glyceraldehyde 3-phosphate dehydrogenase, β-tubulin, calmodulin, actin 1, and translation elongation factor 1α) representing 11 fungal species: Colletotrichum karstii, Cytospora californica, Cytospora joaquinensis, Cytospora parapistaciae, Cytospora pistaciae, Diaporthe ambigua, Didymella glomerata, Diplodia mutila, Neofusicoccum mediterraneum, Phaeoacremonium canadense, and Schizophyllum commune. Pathogenicity tests conducted in the main pistachio cultivars Kerman, Golden Hills, and Lost Hills using the mycelium-plug method indicated that all fungal species were pathogenic to Pistacia vera. All species tested caused cankers in pistachio branches, although virulence among species varied from high to moderate. Overall, N. mediterraneum and Cytospora spp. were the most widespread and virulent species associated with canker diseases of pistachio in California.