Stimulation of Pod and Ovule Growth of Soybean, Glycine max (L.) Merr. by 6-Benzylaminopurine

Flowers at distal nodes on soybean racemes usually fail to setpods and subsequently abscise. Physiological and histologicalstudies were performed to determine the influence of 6-benzylaminopurine(BAP) on distal pod development. The pedicels of fully openedflowers on terminal racemes of field-grown IX93-100 soybeanplants were treated three times with 200 mg kg^-1 BAP in lanolinover a 6-d period. Racemes were then excised and ³²P uptakewas recorded for each flower position within a raceme; histologicalfeatures of pedicels and ovules also were determined. Applicationof BAP increased pod and ovule length, width and weight at allfour distal nodes (D, D-1, D-2, D-3) relative to controls treatedwith lanolin. Length and width of parietal endosperm cells weresmaller in BAP-treated ovules at the most proximal node beingstudied (D-3), and greater numbers of parietal endosperm cellswere observed at D-1 and D-3 nodes when compared to lanolincontrols. Smaller amounts of starch were found in suspensorcells, endosperm, and integuments of lanolin-treated ovules,and starch depletion over time was observed within starch sheathsof pedicels from lanolin-treated pods when compared to BAP-treatedtissues. BAP-treated racemes had more ³²P uptake at the fourmost distal nodes. A higher rate of uptake (cpm mg^-1 f. wt)was evident in ovules than in ovary tissues. These results suggestthat for racemes otherwise destined to abscise, applicationof BAP promotes pod set and growth by stimulating ovule development.Copyright1993, 1999 Academic Press Pod, ovule soybean, abscission, 6-benzylaminopurine     

Seedling-selection effects on morphological traits of mature plants in red clover

Knowledge of the correlation between juvenileand mature-plant traits is critical in determining the opportunities for early stage selection. The effects of early stage selection on mature-plant performance have rarely been quantified. This study was conducted to identify seedling traints in red clover (Trifolium pratense L.) that correlate to mature-plant traits and to evaluate the effect of seedling selection on forage yields and other mature-plant traits. The results showed that relationships between most seedlingand mature-plant traits were weak (r ranged from 0.170 to 0.239). Nevertheless, selecting the top 10% seedlings for petiole length, days from emergence to full expansion of the 4th leaf (D4LE), or leaves per seedling, produced a mature-plant population with higher individual plant dry weight (IPDW1) and higher annual yield in 1993 (Y93). Selection for leaves per seedling increased IPDW1 by 23.2%. Selection for petiole length and the smallest D4LE increased Y93 by 15.7% and 13.8%, respectively. Furthermore, substantial expected genetic gains were obtained for IPDW1 and Y93 when selecting for some seedling traits. We conclude that plants and families with low potential yield can be eliminated at the seedling stage in red clover. This will allow breeders to increase the number of superior plants to be field tested or to conduct a more rigorous evaluation of the selected plants. Among the five selection schemes tested for direct selection of mature-plant traits, mass selection produced the largest genetic gain.     

Methods for the study of cytoplasmic effects on quantitative traits

Summary The methods used to study cytoplasmic effects in quantitative traits often do not measure quantitative genetic parameters, while those that do are either complicated or do not take into account situations where the expression of cytoplasmic effects does not persist, but decreases in advanced generations. We present two simple models that take cytoplasmic effects and the quantitative genetic parameters into account. One of the models (A) is for cases where cytoplasmic effects remain constant through successive generations, and the second model (B) is for traits where cytoplasm-genotype interactions are present. This model also takes into account the decreasing persistence of cytoplasmic effects with advancing generations, which is often reported in the literature.     

Litter dynamics of low and high tannin sericea lespedeza plants under field conditions

Sericea lespedeza [Lespedeza cuneata (Dum. Cours) G. Don.] is a perennial legume with high polyphenol (tannin) concentration. The decomposition and nutrient release of sericea lespedeza residues with two tannin levels (high = 22% or low = 16%), which were either placed on the soil surface or buried at a depth of 5 cm were studied. An experiment was carried out at two sites for 2 yr. Litter mass loss and nutrient (N, P, K, Ca, Mg, Cu, Fe, Mn, Zn, B, Mo, Co) release were recorded. Litter mass loss was higher for the low-tannin residues and for those buried. From the beginning of the experiments, the C : N ratio was lower than 25 : 1 and N was mineralized for most of the studied cases; this means that N increased in availability to plants. The release of the rest of the studied nutrients was higher at the depth of 5 cm than on the soil surface and higher for low-tannin residues than for high-tannin. The observed accumulation of some nutrients in the first months presumably depended on microbial activity. The rate of release was higher for the macronutrients than for the micronutrients, with the exception of B, which had the same behaviour as the macronutrients. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genetic diversity of Crotalaria germplasm assessed through phylogenetic analysis of EST-SSR markers.

The genetic diversity of the genus Crotalaria is unknown even though many species in this genus are economically valuable. We report the first study in which polymorphic expressed sequence tag-simple sequence repeat (EST-SSR) markers derived from Medicago and soybean were used to assess the genetic diversity of the Crotalaria germplasm collection. This collection consisted of 26 accessions representing 4 morphologically characterized species. Phylogenetic analysis partitioned accessions into 4 main groups generally along species lines and revealed that 2 accessions were incorrectly identified as Crotalaria juncea and Crotalaria spectabilis instead of Crotalaria retusa. Morphological re-examination confirmed that these 2 accessions were misclassified during curation or conservation and were indeed C. retusa. Some amplicons from Crotalaria were sequenced and their sequences showed a high similarity (89% sequence identity) to Medicago truncatula from which the EST-SSR primers were designed; however, the SSRs were completely deleted in Crotalaria. Highly distinguishing markers or more sequences are required to further classify accessions within C. juncea.     

Evaluation of Lespedeza germplasm genetic diversity and its phylogenetic relationship with the genus Kummerowia

The genetic diversity of the genus Lespedeza is not well known and the phylogenetic relationship of Lespedeza with the genus Kummerowia is unclear. We report the first study in which polymorphic expressed sequence tag-simple sequence repeat (EST-SSR) markers derived from Medicago, cowpea and soybean were used to assess the genetic diversity of the USDA Lespedeza germplasm collection and clarify its phylogenetic relationship with the genus Kummerowia. Phylogenetic analysis partitioned 44 Lespedeza accessions into three main groups some of which were species-specific and eight subgroups. This data set revealed some misidentified accessions, and indicated that the two species in the genus Kummerowia are closely related to the genus Lespedeza. Morphological reexamination was used to correct the misidentified accessions within the genus Lespedeza. Our results demonstrated that phylogenetic analysis with morphological reexamination provides a more complete approach to classify accessions in plant germplasm collection and conservation.