Association of Botryosphaeria Panicle and Shoot Blight of Pistachio with Injuries of Fruit Caused by Hemiptera Insects and Birds

Panicle and shoot blight of pistachio caused by species of Botryosphaeriaceae fungi remains one of the major diseases of pistachio in California, with the highest potential for crop destruction because buds and fruit clusters (panicles) are killed. Pistachio fruit can also be damaged by various insect pests. For instance, hemipteran insects are considered major pests of pistachio and can attack maturing fruit, causing necrotic areas on the fruit epicarp (epicarp lesion). Surveys in pistachio orchards showed a putative association of punctures of pistachio fruit with infection by Botryosphaeriaceae fungi, resulting in panicle and shoot blight. This study was undertaken to determine any association of Botryosphaeriaceae fungi with fruit bearing epicarp lesions and whether hemipteran insects can actively carry propagules of the pathogens to healthy fruit and cause disease. Three large insects of the order Hemiptera (Thyanta pallidovirens, Acrosternum hilare, and Leptoglossus clypealis) were used in pathogen-spread and infection experiments. The most frequently isolated species of the family Botryosphaeriaceae in pistachio, Neofusicoccum mediterraneum, was used in these transmission experiments. Significantly higher incidence of fruit infected by N. mediterraneum was recorded when pistachio clusters were sprayed with a spore suspension of N. mediterraneum and caged with the above insects than the level of infected fruit sprayed similarly with the pathogen but caged without any insects. Furthermore, increasing the number of insects caged with pistachio clusters resulted in an increase of insect feeding punctures and, subsequently, disease incidence. Similarly, increasing the number of wounds per fruit made with a needle, simulating injuries caused by the insect’s stylet, resulted in significantly higher incidence of infected fruit than for wounded fruit with fewer injured sites. In addition, bird-injured fruit were also associated with higher incidence of panicle blight than fruit not injured by birds, especially in orchards with high disease incidence. In laboratory experiments, wounding or applying fruit sap to nonwounded fruit resulted in significantly higher incidence of infected fruit than in nonwounded fruit without sap. In field experiments, wounding of fruit before or after inoculation with N. mediterraneum resulted in higher disease incidence than nonwounded and inoculated fruit. Additionally, fruit sap enhanced initial mycelial growth of N. mediterraneum. Protecting fruit clusters from injuries by hemipteran insects or birds using mesh cages significantly reduced the incidence of panicle and shoot blight. The association of wounding by hemipteran insects and birds with high incidence of infected pistachio fruit may explain partially the broad distribution of Botryosphaeria panicle and shoot blight among pistachio orchards of the central San Joaquin Valley, even in areas where inoculum sources are not nearby.

Early California Reconsidered

David Weber was the leading scholar of the Spanish Borderlands in the late twentieth and early twenty-first century. Just before his death in 2010, Weber shared a rare interrogation he found in Mexico’s major archive with us. It concerned Jedediah Smith’s California incursion into the Central San Joaquín Valley in 1827–1828. Using digitized databases of Franciscan registers from Mission San José and Mission Santa Clara, we have decoded the interrogation and identified all the Indians questioned, as well as those mentioned in the document, by tribal origin and language affiliation. By lifting the veil of Indian anonymity, we were able to better understand the motivation behind each testimony allowing us to offer, for the first time in the literature, a look at the impact of Jedediah Smith’s expedition from an Indian perspective. Indian interaction (both tribal and Mission) with Mexican and American imperialism is central to understanding Smith’s disruptive impact in California.

Evaluation of Four Pistachio Rootstocks in California's Central Valley

Four pistachio rootstocks, Pistacia atlantica, P. integerrima, and two selections of the same interspecific hybridization, P. atlantica, P. atlantica × P. integerrima (A.K.A. PGII and UCB #1) budded with P.vera, P. vera cv. Kerman females have been evaluated since 1989 in three locations in California's central San Joaquin Valley. Thus far, Atlantica is the most cold tolerant, followed by the interspecific hybrids and Integerrima. Integerrima and UCB no. 1 have produced significantly more clusters and nuts per tree, but all rootstocks have produced the same numbers of nuts per cluster. Trees on no.1 and Integerrima rootstocks also have produced significantly more kilograms of nuts per trunk cross sectional area than Atlantica and PGII. UCB #1 and Integerrima also are significantly more tolerant of the soilborne fungus Verticillium dahl. All rootstocks are equally infected with three species vesicular–arbuscular mycorrhizzae. Two seasons of irrigation with water up to 8.00 dS·m–2, have not affected rootstock performance or yield. UCB #1, Integerrima, and PGII all require supplemental boron, zinc, and copper nutrition for good production. Thus far, Integerrima is the best rootstock for soils with verticillium infestations unless winter temperatures are frequently below freezing. UCB #1 is the best rootstock for locations with cold winters.

Comparison of Four Pistachio Rootstocks in California

Currently, the California pistachio industry relies on four rootstocks: two species and two interspecific hybrids—P. atlantica, P. integerrima, P. integerrima × P. atlantica, and P. atlantica × P. integerrima. The first three are open-pollinated, the last is the result of a closed pollination. The objective of these long-term trials is to compare rootstock behavior in the three major pistachio-producing regions of California. Three trials of 100 replications consisting of one of each of the four rootstocks were established in the three major growing regions of California in 1988. All the rootstocks in all three locations were budded with buds from the same female and male trees. Thus, all differences in performance are the result of rootstock or local climate. Results thus far demonstrate that rootstocks with P. atlantica as the maternal parent are more cold tolerant; more efficient in boron, zinc, and copper uptake; less vigorous; less precocious; and more susceptible to V. dahliae than rootstocks with P. integerrima as the maternal parent. The results also demonstrate that pistachios in California's southern San Joaquin Valley will bear 1 year ahead of pistachios in the central San Joaquin Valley or the northern Sacramento Valley. Trees on rootstocks with P. integerrima parentage also bear earlier than trees on P. atlantica and have higher yield efficiencies. All are colonized by vesicular–arbuscular mycorrhizae.