T. Austin Campbell

Comparisons of genetic and morphological distance with heterosis between Medicago sativa subsp. sativa and subsp. falcata

Biomass yield heterosis has been shown to exist between Medicago sativasubsp. sativa and Medica gosativa subsp. falcata. The objective of this study was to gain a better understanding of what morphological and genetic factors were most highly correlated with total biomass yield heterosis. We calculated genetic distances among nine sativa and five falcate genotypes based on amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) DNA markers. Genetic distance did not correlate with specific combining ability (SCA) or mid-parent heterosis. In contrast, a morphological distance matrix based on seventeen agronomic and forage quality traits was significantly correlated with heterosis; the agronomic traits of maturity, midseason regrowth, and autumn regrowth showed strong association with heterosis. Heterosis was also correlated with subspecies. We suggest that in many cases progeny heterosis can be accounted for by the interaction of genes controlling morphologically divergent traits between the parents. In other cases, progeny heterosis could also be due to divergence between the parents at particular genetic loci that do not control field-level phenotypic differences. Genetic distanceper se between parental genotypes, based on neutral molecular markers, however, does not reflect the potential of individual genotypes to produce heterosis in their progeny.

Differential responses of alfalfa cultivars to aluminum stress

Abstract Toxic levels of aluminum can cause severe yield reduction in alfalfa (Medicago sativa L.), especially in the presence of drought stress. Reactions to Al stress of alfalfa cultivars and germplasms, representing a broad genetic base and the entire range of dormancy types, were evaluated in a Monmouth soil study [26.2% Al saturation (pH 4.8) vs 2.8% Al saturation (pH 5.7)] and in two nutrient solution experiments (0 vs 111 μmol Al; pH 4.5). The soil study, Experiment 1, and Experiment 2 were harvested 28, 40, and 25 d after seeding, respectively. In all studies, entries differed significantly in vigor and yields were reduced significantly by Al stress. In the soil study, only ‘Lahontan’ was not affected significantly by Al stress, although Lahontan, ‘Atlantic’, ‘B13‐A14’ (tolerant check), ‘Ladak 65’, and ‘Mesa‐Slrsa’ had comparable relative weights (dry weight stressed/dry weight unstressed). There were no statistically significant differential responses to Al stress in Experiment 1, however the rel...

Delayed light emission and fluorescence responses of plants to chilling

Abstract Delayed light emission (DLE) of chlorophyll has the same excitation and emission spectra as chlorophyll fluorescence and was formerly called delayed fluorescence. DLE has a much longer time response than true chlorophyll fluorescence and is detectable for times ranging from milliseconds to many minutes. DLE is induced by back reactions of the photosynthetic pathway and therefore requires functional chloroplasts. It is detectable only in the dark following light excitation, yields very low energy, and decays very rapidly. DLE repetitively excited over time, which we term refreshed DLE (RDLE), shows a shoulder and broad peak in our measurements, indicating participation of at least two energy pools. DLE is altered by physiological stresses that affect chloroplasts or photosynthesis, and as illustration, plant species known to be very susceptible or very tolerant to chilling were exposed to chilling temperatures for varying times. RDLE at 0.3 s (the initial shoulder on our curves) rose in response to chilling damage in the susceptible species. The major RDLE peak was greatly inhibited in the susceptible species and showed only small changes in the tolerant species. Fluorescence measurements made on the chilling-tolerant species indicated similar responses and similar coefficients of determination were derived. These results indicate that measurement of precisely timed delayed light emission or of refreshed delayed light emission at a less precisely controlled time can be used to detect chilling stress.

Differential responses of red clover germplasms to aluminum stress.

Abstract Toxic levels of aluminum can cause severe yield reduction in red clover (Trifolium pratense L.), especially in the presence of drought stress. Aluminum tolerances of 17 red clover cultivars and germplasms representing a broad genetic base were evaluated in a Monmouth soil [26.2% Al saturation (pH 4.8) vs. 2.8% Al saturation (pH 5.7)] and in nutrient solutions (0 vs 111 μM Al; pH 4.5). The soil and nutrient culture studies were harvested 29 and 27 d after seeding, respectively. Aluminum stress reduced shoot and root growth significantly in soil but not in nutrient culture. Entries differed significantly in shoot vigor in both media and in root vigor in nutrient culture; responses to the two media were positively correlated. Relative weights (dry weight stressed/dry weight unstressed) in soil and nutrient culture were not correlated. In soil, Al stress significantly reduced shoot growth of all entries except ‘Tristan’, whereas root growth was not affected significantly in ‘Atlas’, ‘Lakeland’, ‘Pers...

Differential responses of sericea lespedeza to aluminum stress

Abstract Toxic levels of aluminum can cause severe yield reductions in many crop species, but sericea lespedeza [Lespedeza cuneata (Dum.‐Cours.) G. Don] has demonstrated considerable tolerance. Aluminum tolerances of six sericea lespedeza cultivars (Am 312, Appalow, AU Lotan, Interstate, Interstate 76, Serala) representing a broad genetic base were evaluated in a Monmouth soil [26.2% Al saturation (pH 4.8) vs. 2.8% Al saturation (pH 5.7)] and in nutrient solutions (0 vs 111 μM Al; pH 4.5). The soil and nutrient culture studies were harvested 30 and 27 d after seeding, respectively. Aluminum stress did not reduce root and shoot growth significantly, nor were the pooled Al stress x cultivar interactions significant. Cultivars differed significantly in mean shoot and root vigor in nutrient solutions but not in soil. R‐esponses in soil were only weakly correlated with responses in nutrient solutions. Am 312 and Appalow had the lowest relative weight values (dry weight stressed/dry weight unstressed) in both m...

Agronomic evaluations of grass and legume forage species collected in the Xinjiang Autonomous Region of the People's Republic of China and Mongolia

Because rangelands in the Xinjiang Autonomous Region of thePeoples Republic of China (PRC) and Mongolia are typicallyseverely overgrazed, bilateral (U.S./ PRC, U.S./Mongolia)efforts have been initiated to expedite capture of the remaining geneticdiversity. The current study was designed to evaluate selected germplasm of thefollowing forage species collected in these threatened areas: Bromusinermis Leyss., Dactylis glomerata L.,Festuca arundinacea Schreb., Festucaovina L., Festuca rubra L., Phleumphleoides (L.) Karsten, Phleumpratense L., Poa palustris L., Poapratensis ssp. angustifolia (L.) H.Lindb., Medicago sativa ssp. falcataArcengeli, Medicago sativa L. ssp. sativa, Medicago lupulina L.,Medicago ruthenica (L.) Ledebour,Trifolium fragiferum L., Trifoliumlupinaster L., Trifolium pratense L., andTrifolium repens L. Accessions were evaluated in the fieldat Beltsville MD (USA) on an Iuka sandy loam(coarse-loamy, siliceous, acid, thermic, Aquic Udigluvent; pH6.5) in a two-year study. Comparative check cultivars were included.There was significant variation in days to 50% heading (grassspecies) or flowering (legume species), leaf texture (grassspecies), growth habit, spring vigor, and dry matter yield among accessionsof at least some genera. Accessions did not demonstrate higher diseasesusceptibility relative to check cultivars, except in the case of severalF. arundinacea and oneM. sativa ssp.falcata entries. There was no significant variation in leafshape among the legume accessions, nor were leaf shapes significantly differentfrom those of the check cultivars. Several F.ovina, F. rubra,and Poa pratensis accessions may have potential in turfgrass breeding programs. There were apparent positive relationships amongupright growth habit, spring vigor, late development, and yield.