SUMMARYPresence of the endophytic fungus Acremonium coenophialum Morgan-Jones and Gams in tall fescue {Festuca arundinacea Schreb.) enhances host persistence in drought-prone environments. However, the physiological mechanism is not well understood. We investigated the influence of endophyte infection and water deficit on osmotic adjustment, stomatal conductance, tiller survival and leaf elongation rate of genotype GA87-122 and cv. Kentucky-31 {KV31) of tall fescue. Plants were grown in a greenhouse in pots containing fine-si!ty topsoil {experiment 1) or sand (experiment 2). In expt 1, endophyte-infected (El) and endophyte-free (EF) isolines of GA87-1 22 were exposed to two drought preconditioning cycles, after which all pots were re-watered and osmotic adjustment determined. Osmotic adjustment was -0-46 and -0-51 MPa in El leaf blades and tiller bases and -0-29 and -0-13 MPa in EF leaf blades and tiller bases, respectively. In expt 2, El and EF GA87-122 and KY31 were exposed to severe drought after two preconditioninjj cycles, then re-waiered. During the second preconditioning drying cycle of KY31, stomatal conductance tended to be lower in El than in EE plants, but the difFerence was significant (P ^ 0-05) only at two sampling times. Shoot tissues osmotically adjusted 017-0-31 MPa more in FJ than in FF plants. Tiller survival and leaf elongation rates were higher (P ^ 0-05) in preconditioned El than in EF plants. Basal-zone osmotic adjustment was correlated with tiller survival rate in GA87-122 and KY31 {r = 0-87, F ^ O' Ol for both). Enhanced osmotic adjustment in the meristematic and growing zone might account for improved survival of tillers by facilitating protection of the apical meristem.

Emphysiology of the endophyte (Acremonium coenophialum Mor· gao-Jones and Gams)-tall fescue (Festuca arundinllcea Schreb.) as· soci~1tion needs to be understood in order to promote environmental fitness traits of the association while reducing its deleterious effects on ruminants. Our objective was to determine the influence of en· dophyte on drought stress tolerance, persistence, and yield components of field-grown tall fescue on a Typic Hapludalfs soil. A water supply gradient was established during 1988 and 1989 with line-source irrigation on established populations ofO and 80o/o endophyte-infected tall fescue. Whole plots consisted of endophyte infection status, across whi<:h a gradient of water was applied in a strip-split fashion with eight replicates. Tiller population density and herbage yield were determined every 28 d and yield components were measured on selected dates. Relative to populations receiving high irrigation (375...{;50 mm applied), tiller density in nonirrigated stands (0-50 mm applied) from July to October 1988 was reduced an average of 42% in infected tall fescue and 55% in noninfected tall fescue. Tiller density of nonirri· gated, infected populations recovered fully to that of high irrigation treatments by 17 November, whereas that ofnonirrigated, endophyte· free populations recovered to only 62% of irrigated treatments. The advantage in population density due to endophyte infection continued throughout 1989, a relatively wet year. A benefit in total forage yield due to endophyte infection was not consistently evident because of greater yield per tiller in endophyte-free stands in 1989. Enhanced tiller density and survival were associated with endophyte infection during severe water deficit, and this advantage continued throughout the subsequent year. Endophyte infection confers population stability in tall fescue during drought stress through improved tiller and whole plant survival.

In a 2 × 2 × 2 factorial experiment, plants of one genotype of tall fescue (Festuca arundinacea) were grown in soil in pots in a glasshouse on two occasions. The treatments were either with (E+) or without (E–) infection by the fungal endophyte Neotyphodium coenophialum; with (N+) or without (N–) inoculation by the root‐knot nematode Meloidogyne marylandi; and with or without water deficit stress. In the first experiment, nematode numbers after 5 weeks had increased 10 times in the E–/N– watered pots and 22 times in the E–/N+ stressed plants. Root dry weight was decreased in all E–/N+ pots, compared with E–/N–. In contrast, nematode numbers in all E+/N+ pots decreased to nearly zero and root dry weight was unaffected. Osmotic adjustment in the growing zone of stressed plants was –0·35 MPa in E–/N– pots, but only –0·10 MPa in E–/N+ pots. Osmotic adjustment was greatest (–0·64 MPa) in E+ pots of both nematode treatments and almost no nematodes survived in the N+ pots. In the second experiment, there was complete nematode mortality in the E+ pots. Plant water relations were unaffected by treatments, however. It is concluded that endophyte‐enhanced persistence of tall fescue in M. marylandi‐infested soils that are prone to drought may be explained at least partly by endophyte protection of roots from nematode damage. Nematode inhibition by the endophyte may operate in addition to direct influences of the endophyte on enhancing drought tolerance of the host.

A total of 17 vegetable-type soybean (Glycine max [L.] Merr) genotypes were planted in four-row plots arranged in a randomized complete block design in 1988 and 1989 at Petersburg, Virginia. Each genotype was harvested at four developmental stages and evaluated for phytate content. Highly significant differences for phytate content were observed among the stages of harvest and genotypes, and there was an interaction between genotype x stage of harvest. The significant differences observed for phytate content among genotypes indicated that genetic variation exists among the tested genotypes for selection and improvement through hybridization. Among the genotypes, 'Kingston' and PI 423852 had the highest phytate content in most stages of harvest while PI 416771, 'Emperor', and PI 416982 had the lowest phytate values. A heritability estimate of 81 percent was observed for phytate content. This high heritability value indicates that selecting genotypes for lower phytate content would be effective. Significant correlations were observed for phytate content among genotypes harvested at R6, R7, R8, and overall. The magnitude of association of R6 with the overall phytate mean was especially high. These results illustrate that determining the phytate content of genotypes at the R6 growth stage would be a good predictor of the overall genotypic performance.