‘UCB-1’ (Pistacia atlantica × Pistacia integerrima) rootstock is a hybrid cultivar widely used by the U.S. pistachio industry. In the last three years, a large number of micropropagated UCB-1 pistachio rootstocks planted in California and Arizona orchards exhibited shortened internodes, stunted growth, swollen lateral buds, bushy/bunchy growth, stem galls with multiple buds, and twisted roots with minimal lateral branching. Field T-budding success in affected orchards was reduced to approximately 30% with unusual bark cracking often observed around the bud-union. The percentage of abnormal rootstocks within affected orchards varied from 10 to 90%. We have termed the cumulative symptoms “pistachio bushy top syndrome” (PBTS) to describe these affected trees. Two isolates, both containing virulence factors from the phytopathogen Rhodococcus fascians, were identified on symptomatic trees in field and nursery samples. Micropropagated UCB-1 trees inoculated with the Rhodococcus isolates exhibited stunted growth, shortened internode length, swollen lateral buds, sylleptic branching, and differences in root morphology, compared with control UCB-1 trees. To our knowledge, this is the first report of Rhodococcus isolates, related to Rhodococcus fascians, causing disease on a commercial tree crop and the results presented indicate that this organism is responsible at least in part for PBTS in California and Arizona.

Pistachio (Pistacia vera L.) trees from the National Clonal Germplasm Repository (NCGR) and orchards in California were surveyed for viruses and virus-like agents by high-throughput sequencing (HTS). Analyses of sequence information from 60 trees identified a novel virus, provisionally named “Pistachio ampelovirus A” (PAVA), in the NCGR that showed low amino acid sequence identity (approximately 42%) compared with members of the genus Ampelovirus (family Closteroviridae). A putative viroid, provisionally named “Citrus bark cracking viroid-pistachio” (CBCVd-pis), was also found in the NCGR and showed approximately 87% similarity to Citrus bark cracking viroid (CBCVd, genus Cocadviroid, family Pospiviroidae). Both PAVA and CBCVd-pis were graft transmissible to healthy UCB-1 hybrid rootstock seedlings (P. atlantica × P. integerrima). A field survey of 123 trees from commercial orchards found no incidence of PAVA but five (4%) samples were infected with CBCVd-pis. Of 675 NCGR trees, 16 (2.3%) were positive for PAVA and 172 (25.4%) were positive for CBCVd-pis by reverse-transcription polymerase chain reaction. Additionally, several contigs across multiple samples exhibited significant sequence similarity to a number of other plant virus species in different families. These findings require further study and confirmation. This study establishes the occurrence of viral and viroid populations infecting pistachio trees.

The daily (24-hour)

Colletotrichum Corda, 1831 species are well-documented pathogens of citrus that are associated with leaf and fruit anthracnose diseases. However, their role in twig and shoot dieback diseases of citrus has recently become more prominent. Recent surveys of orchards in the Central Valley of California have revealed C. gloeosporioides and a previously undocumented species, C. karstii, to be associated with twig and shoot dieback. Pathogenicity tests using clementine (cv. 4B) indicated that both C. karstii and C. gloeosporioides are capable of producing lesions following inoculation of citrus stems. Pathogenicity tests also revealed C. karstii to be the most aggressive fungal species producing the longest lesions after 15 months. The majority of spores trapped during this study were trapped during or closely following a precipitation event with the majority of spores being trapped from January through May. These findings confirm C. karstii as a new pathogen of citrus in California.

No abstract

The utility of water production models as irrigation management tools is dependent upon their accuracy. Development of precise water production models requires a thorough understanding of how water and other factors interact to affect plant growth and yield. The objective of this experiment was to identify significant environmental variables which control water production function (transpiration vs. yield) variability between harvests and seasons for alfalfa (Medicago sativa L.) over a seven year (1981)(1982)(1983)(1984)(1985)(1986)(1987) period in northwestern New Mexico. A single line-source design was used to supply a continuous gradient of irrigation (I) to the crop, and transpiration (T) was calculated as the difference between evapotranspiration, as estimated by the water balance method, and modeled soil water evaporation at each I level. Yield per cutting was found to be a function of T, growing degree-day accumulation, average daily solar radiation, year and harvest number within year. A multiple regression equation formulated with these variables explained 82% of the yield variability. Average yield per cut in 1981 at 50 mm ofT was 1 Mg ha -1 and in 1985 at the same level of T was 2 Mg ha-1 based on the regression model. Yield per cut at any given level of T, as estimated by the coefficients of this equation reached a maximum at year 5.7 and a minimum in year 1. Within a season, yield per unit T was generally greatest at cut 1 and lowest at cut 2. Total seasonal yield was found to be a function of T and year which explained 90% of yield variability. Yield varied from 0.83 Mg ha-1 to 18.1 Mg ha-1 and T varied from 186 mm to 1298 mm.A positive linear relationship between alfalfa (Medicago sativa L.) yield (Y) and water, as evapotranspiration (ET) or transpiration (T), has been recognized by various researchers (Bauder et al. 1978;Retta and Hanks 1980;Sammis 1981;Wright 1988). As pointed out by Vaux and Pruitt (1983) however, parameters of the water producOffprint requests to." D. Smeal tion function (relationship between Y and ET, or T) are generally site and crop (or cultivar) specific. Hanks and Retta (1980) also recognized variability in the water production function between years. The prospects then are poor for developing a predictively useful, single variable, mathematical relationship between yield and water-use that is applicable among multiple harvests and years (Highstreet et al. 1987;Undersander 1987;Wright 1988). For water-production models to be accurate irrigation management tools, they must consist of complex multivariate functions that consider environmental characteristics and crop physiological development. These models could then assist irrigators in their effort to maximize water-use efficiencies and economic returns. The objective of this research was to develop a water production function for alfalfa that is applicable over a seven year period at Farmington, NM. The independent variables considered were: harvest number; year; average daily solar radiation for growing period (Sa) or...

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.

If you as the grower can recognize the different types of scars you can differentiate between symptoms that indicate biological (e.g., insect, mite, disease, or snail), mechanical (e.g., equipment, hail, or wind rubbing), or chemical (e.g., phytotoxic burn) damage. Once you know the causal agent you can take steps to reduce injury to future crops. Orchards should be carefully monitored when fruit are small, the stage at which damage is most likely to occur. As soon as you observe signs of damage, make an immediate search for possible sources of the damage. It is much harder to determine the cause of fruit damage toward the end of the season because the insects or other causal agents are no longer present in the orchard and many types of injuries are by then similar in appearance. PUBLICATION 8090 Most citrus fruit scarring occurs in spring (April through June) when fruit are first developing on the tree. The rind tissue is very tender and easily damaged at this time. If damage is severe, the fruit will often fall off of the tree, either at the time of damage or during June fruit drop. If the damage is less severe, the fruit will remain on the tree and continue to grow, and the scarring will become noticeable. Some of the more common types of fruit damage seen in citrus groves are shown on the pages that follow.