In 2006, 2007, and 2008, we sampled 257 isolates of Phytophthora capsici from vegetables at 22 sites in four regions of New York, to determine variation in mefenoxam resistance and population genetic structure. Isolates were assayed for mefenoxam resistance and genotyped for mating type and five microsatellite loci. We found mefenoxam-resistant isolates at a high frequency in the Capital District and Long Island, but none were found in western New York or central New York. Both A1 and A2 mating types were found at 12 of the 22 sites, and we detected 126 distinct multilocus genotypes, only nine of which were found at more than one site. Significant differentiation (FST) was found in more than 98% of the pairwise comparisons between sites; approximately 24 and 16% of the variation in the population was attributed to differences among regions and sites, respectively. These results indicate that P. capsici in New York is highly diverse, but gene flow among regions and fields is restricted. Therefore, each field needs to be considered an independent population, and efforts to prevent movement of inoculum among fields need to be further emphasized to prevent the spread of this pathogen.

Because of their microscopic size, the forcibly ejected spores of ascomycete fungi are quickly brought to rest by drag. Nonetheless some apothecial species, including the pathogen Sclerotinia sclerotiorum, disperse with astonishing rapidity between ephemeral habitats. Here we show that by synchronizing the ejection of thousands of spores, these fungi create a flow of air that carries spores through the nearly still air surrounding the apothecium, around intervening obstacles, and to atmospheric currents and new infection sites. High-speed imaging shows that synchronization is self-organized and likely triggered by mechanical stresses. Although many spores are sacrificed to produce the favorable airflow, creating the potential for conflict among spores, the geometry of the spore jet physically targets benefits of the airflow to spores that cooperate maximally in its production. The ability to manipulate a local fluid environment to enhance spore dispersal is a previously overlooked feature of the biology of fungal pathogens, and almost certainly shapes the virulence of species including S. sclerotiorum. Synchronous spore ejection may also provide a model for the evolution of stable, self-organized behaviors.hydrodynamics | cooperation | fungal spores T he forcible launch of sexual spores into dispersive air flows enables ascomycete fungi to propagate between physically distant patches of habitat; for example, the pathogen Sclerotinia sclerotiorum disperses from apothecia in the ground to infect the flowers of crop plants (1), and dung fungi in the genus Ascobolus must escape from their dung piles to be ingested by animals (2, 3). Although their microscopic size enables spores to be transported by even slow flows of air, it also severely limits the distance that they may travel ballistically. Launched at a speed of 8.4 m·s −1 , the 12 μm long spores of S. sclerotiorum would be decelerated to rest after traveling less than 3 mm (4, 5). In response to this constraint, fungi have evolved multiple adaptations to maximize spore range. For example, spores that cohere during launch benefit from increased inertia (6), while individually ejected spores may be shaped in order to minimize drag (5).Here we demonstrate the remarkable ability of apothecial fungi to manipulate their own fluid environment and negate the range constraints imposed by fluid drag. It has long been known (7,8) that in many species spore discharge is almost synchronous between the asci of an individual apothecium, so that hundreds, thousands, or tens of thousands of spores can be discharged in a single puff, lasting a fraction of a second (Fig. 1 A, B). Discharge may be initiated spontaneously, or by changes in air pressure, or when an apothecium is touched. Buller (9) first connected spore coejection with the creation of a flow of air. In this work we adapt algorithms originally developed to simulate hundreds of thousands of droplets in clouds to prove that the hydrodynamic cooperation of spores creates a flow of air. Our simulations, analytic models,...

Studies were initiated in 1988 and 1991 to assess long-term survival ability of Colletotrichum coccodes. Sclerotia and infected tomato fruit skin tissue were enclosed in nylon pouches and placed on the soil surface (0 cm) or buried 10 and 20 cm deep in fields located in Geneva, New York. Over time, the greatest decline in recovery of C. coccodes from tomato skin and decrease in viability of sclerotia were from samples placed on the soil surface. In the 1988 study, after 8 years in the field, 0, 90, and 88% of the sclerotia were viable, and C. coccodes was isolated from 0, 54, and 86% of the tomato skin tissues at the 0-, 10-, and 20-cm soil depths, respectively. In the 1991 study, after 5 years in the field, C. coccodes was isolated from 22, 35, and 37% of the tomato skin tissues, and 55, 91, and 92% of the sclerotia were viable at the 0-, 10-, and 20-cm soil depths, respectively. It is apparent that lengthy crop rotations are required to significantly decrease viable inoculum of C. coccodes. In a separate study, C. coccodes overwintered in naturally infected tomato roots in commercial fields and was consistently isolated from roots in the fall and the following spring. Fields sampled in the fall yielded similar numbers of plants with infected roots the following spring.

Alfalfa is a source for viruses that may be acquired by aphids and transmitted to snap bean, Phaseolus vulgaris L. Snap bean Þelds in proximity to alfalfa could have an increased risk of virus infection. Knowledge of the abundance and temporal and spatial dispersal patterns of commonly encountered aphids in commercial snap bean Þelds, varying in distance from alfalfa, could provide insight into this risk. Alate aphids were monitored using water pan traps in snap bean and alfalfa Þelds that were adjacent to or Ͼ1 km away from each other. The pea aphid, Acyrthosiphon pisum (Harris), was the most common aphid species captured in early-planted snap bean Þelds in 2002 and 2003 (56 and 23% of total, respectively), whereas the corn leaf aphid, Rhopalosiphum maidis (Fitch), also was common in 2003 (15% of total). In contrast, the yellow clover aphid, Therioaphis trifolii (Monell), and soybean aphid, Aphis glycines Matsumura, were the most abundant species trapped in late-planted snap bean Þelds in 2002 (77% of total) and 2003 (64% of total), respectively. These species were prevalent in traps in alfalfa as well. The abundance and temporal dispersal patterns of these species in snap beans adjacent to and Ͼ1 km away from alfalfa were similar, suggesting that the risk for virus infection may not be affected by proximity to alfalfa. A similar number of alate aphids also were captured along snap bean Þeld edges and Þeld centers, regardless of their proximity to alfalfa. This suggests that the aphids dispersed into snap bean randomly rather than directionally from the Þeld edge. The implication of these results is that separating snap bean Þelds from alfalfa or using crop borders/barriers are not likely to be successful virus management strategies.