The Fall Armyworm is a serious pest of many crops throughout most of the Western Hemisphere particularly those belonging to the family Gramineae. This pest is usually controlled by insecticides which, however, cause many health and environmental problems. Although a rich bank of sorgum germplasm occurs in Yemen, no effort has been made to identify the Yemeni cultivars which might express resistance to armyworm attack. There is very little information to show at what time of the growing season and at what planting stage the sorghum cultivars are most susceptible to armyworms. Therefore, eight Yemeni and two American sorghum cultivars were planted in Tucson, Arizona, during 1983 and 1984. The experimental design was a randomized complete block arranged in split-split plots with four replications. The main plots were the varieties, and subplots were two planting dates and two infestation times. The plants were artificially infested with laboratory reared, first instar larvae. Infestation consisted of five larvae per plant in 1983 and ten in 1984. Results demonstrate the 'IBB' and 'TURBA' received the least leaf damage and 'SGIRL-MR1' and 'ALBAIDA' received the most in 1983. However, during 1984, 'TURBA' and 'HAIDRAN' showed the greatest degree of resistance and 'SGIRL-MR1', 'AMRAN', 'ALMAHWIT', and 'ALBAIDA' the least.

Phellinus weirianus (Aphyllophorales: Hymenochaetaceae) causes a white heartrot of living Juglans and is the major cause of decay in Arizona black walnut. Infection is caused by germinating basidiospores. Tissue isolates fruit in culture, but single basidiospore isolates do not. The growth of tissue and single-spore isolates is slow to very slow. Cultural morphology is quite variable even among single-spore isolates derived from a single, culturally produced basidiocarp. Single-spore isolates, presumed to be homokaryotic, are derived from uninucleate spores that germinate and develop hyphae with paired nuclei. Lack of fruiting in homokaryons suggests that P. weirianus is heterothallic. Tissue isolates derived from basidiocarps produced in nature are assumed to be heterokaryotic. Hyphae of tissue isolates have nuclei that are not paired and are more numerous than those in single-spore isolates. Interaction zones are formed in pairings of heterokaryons, pairings of homokaryons, and pairings of homokaryons with the parent heterokaryon. Homozygous matings do not form an interaction zone. Agar-block decay tests show that single-spore isolates exhibit no appreciable differences in decay capacity from tissue isolates. Phellinus weirianus readily decays woods of associated riparian species (Arizona alder, velvet ash, southwestern chokecherry, netleaf oak, and Arizona sycamore) in standard wood test blocks although it is not known on these hosts in nature.

Water relations in cotton plants infected with Phymatotrichum omnivorum were studied to determine the mechanism of wilt development. Relationships between leaf water and osmotic potentials, relative water contents, and diffusive resistances of leaves from diseased and waterstressed healthy plants were similar, indicating that wilting was not due to changes in leaf osmotic regulation. Rates of recovery from wilting, measured as increases in relative water content with time in both diseased and waterstressed healthy plants were identical. There was no significant difference in root dry weight of healthy and diseased plants, indicating that wilting is not a consequence of reduced root area. Resistance to water flow in roots and lower stems increased significantly over those of healthy plants as upper leaves of diseased plants began to wilt. However, resistance to water flow in petioles of diseased plants was unchanged. These results show that wilting in cotton plants is probably the consequence of increased resistance to water flow in roots. Results of a preliminary study indicate that a high-molecular-weight substance produced by the fungus in culture may cause blockage of xylem elements in roots and lower stems and contribute to the increased resistance to water flow.

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Thirty-four cultivars of pea (Pisum sativum) were assayed for tumorigenesis after inoculation with Agrobacterium tumefaciens strain B6. The response of the 34 cultivars fell into 3 significantly different groups based on tumor weights: high, medium, and low susceptibility. The least susceptible cultivar, Sweet Snap, also formed the smallest tumors in comparison to 5 other cultivars when inoculated with 5 other strains of Agrobacterium. Preliminary experiments indicate that neither chemotaxis, binding, vir-gene induction, nor T-DNA expression are limiting factors in Sweet Snap's reduced susceptibility. In an inheritance study, the F1, F2, and F3 progeny from an initial cross between Sweet Snap and Wando (a more susceptible cultivar) formed tumors that were intermediate in weight between the two parents.