Fusarium verticillioides can be seed transmitted and cause systemic infection of maize; however, the frequency of these phenomena has varied widely among and within individual studies. In order to better understand this variability, we evaluated the effect of temperature on the first step in the systemic infection process, the transmission of F. verticillioides from seed to seedling. Seed of a commercial maize hybrid were inoculated with a strain of F. verticillioides that had been transformed with a gene for green fluorescent protein (GFP). The seed were planted in a greenhouse potting mix and incubated in growth chambers. Plants were incubated at one of three temperature regimes designed to simulate average and extreme temperatures occurring in Iowa during the weeks following planting. Root, mesocotyl, and stem tissues were sampled at growth stages V2 and V6, surface disinfested, and cultured on a semiselective medium. At V2, >90% of root and mesocotyl tissues was infected by the GFP-expressing strain at all three temperature regimes. Also at V2, infection was detected in 68 to 75% of stems. At V6, infection of root and mesocotyl tissues persisted and was detected in 97 to 100% of plants at all three temperature regimes. Plants also had symptomless systemic infection of belowground and aboveground internodes at V6. Infection of the three basal aboveground internodes was 24, 6, and 3% for the low-temperature regime; 35, 9, and 0% for the average-temperature regime; and 46, 24, and 9% for the high-temperature regime. Seed transmission and systemic infection occurred at all temperatures and did not differ significantly among treatments. These results indicate that, if maize seed is infected with F. verticillioides, seed transmission is common and symptomless systemic infection can be initiated under a broad range of temperature conditions.

We report a previously undescribed seed-storing behavior of banner-tailed kangaroo rats (Dipodomys spectabilis) that reduces losses to microbes. D. spectabilis cuts upper stems of the grass Sporobolus cryptandrus into 3-to 5-cm sections that we refer to as seed stems. Seeds within these seed stems remain attached to their rachis and are protected by an enveloping leaf. Most seed stems are bundled together tightly in packs of about 50 to several hundred individual stems and jammed vertically into cul-de-sacs excavated in the walls of their burrows. This behavior reduces rate of infection of seeds by fungi and also may reduce number of seeds pilfered by arthropods. Furthermore, compared with seeds of S. cryptandrus housed in middle sections of seed stems, those housed in the ends had a higher rate of infection. Simulated seed stems of wheat straw containing seeds of white millet (Panicum miliaceum) had a lower rate of infection and fewer species of fungi than seeds only protected by wire mesh. Seeds closer to the top of the simulated seed stems were more likely to be infected and had more species of fungi. Community structure and dynamics of microfungi also appeared affected by the protective layering of seed stems. We suggest that D. spectabilis manages the structure, and perhaps dynamics, of communities of microbes within their food caches by modifying position, location, or organization of food items.Key words: caching behavior, Dipodomys spectabilis, kangaroo rat, storing strategies Food storing occurs in a variety of ways by a variety of organisms (Smith and Reichman 1984;Vander Wall 1990). Banner-tailed kangaroo rats (Dipodomys spectabilis; Heteromyidae) are predominantly seed-storing rodents that construct large underground burrow systems where they cache vast amounts of food (Mun and Whitford 1990;Vorhies and Taylor 1922). These caches usually attract a diversity of microbes (Hawkins 1992; and microarthropods (Hawkins and Nicoletto 1992;Seastedt et al. 1986).While studying populations of microfungi that inhabit caches of D. spectabilis at Sevilleta National Wildlife Refuge, Socorro County, New Mexico, we happened on * Correspondent: jherrera@truman.edu caches of food containing large numbers of cut stems containing seeds of the sand dropseed (Sporobolus cryptandrus-Herrera 1996). These seed stems were bundled tightly upright and squeezed into cul-desacs dug in walls of the burrow (Fig. 1).Although we suspect that cutting and carrying stems containing seeds of S. cryptandrus allows D. spectabilis to transport seeds efficiently to their burrow, we were interested in determining why D. spectabilis organizes and places seed stems upright in their burrow. We believe that careful organization of the seed stems of S. cryptandrus is time consuming and energetically costly and suspect the existence of an equally powerful counterselective advantage(s) to the food-storing behavior of the rodent. We investigated whether seeds of S. cryptanDownloaded from https://academic.oup.

Fusarium species are ubiquitous and many times the strains used in an experiment are indistinguishable from those that already exist in the environment. This problem has made it necessary to use methods to "mark" strains. Vegetative compatibility, p-glucuronidase (GUS), and green fluorescent protein (GFP) are a few of the approaches used to mark fungal strains in order to study plant-pathogen interactions. All three methods have previously been used to study Fusarium species (Munkvold and Carlton 1997, Munkvold et al. 1997, Oren et al. 2001, Yates et al. 1999). These tools have facilitated detection and identification of different Fusarium strains in vitro and in planta. Vegetative compatibility can be utilized as a marker because clones of a strain are self-compatible. Vegetative compatibility is based on the ability of fungal strains to produce heterokaryons. Heterokaryon production between strains is controlled by vegetative incompatibility (vie) loci (Correll et al. 1987). Strains of the same species that successfully produce heterokaryons are placed in vegetative compatibility groups (VCGs) (Leslie 1993). Fungi that are incompatible cannot produce heterokaryons and may act antagonistically