Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate

Summary Which factors cause fast-growing plant species to achieve a higher relative growth rate than slow-growing ones? To answer this question 24 wild species were grown from seed in a growth chamber under conditions of optimal nutrient supply and a growth analysis was carried out. Mean relative growth rate, corrected for possible ontogenetic drift, ranged from 113 to 356 mg g^–1 day^–1. Net assimilation rate, the increase in plant dry weight per unit leaf area and unit time, varied two-fold between species but no correlation with relative growth rate was found. The correlation between leaf area ratio, the ratio between total leaf area and total plant weight, and relative growth rate was very high. This positive correlation was mainly due to the specific leaf area, the ratio between leaf area and leaf weight, and to a lesser extent caused by the leaf weight ratio, the fraction of plant biomass allocated to the leaves. Differences in relative growth rate under conditions of optimum nutrient supply were correlated with the soil fertility in the natural habitat of these species. It is postulated that natural selection in a nutrient-rich environment has favoured species with a high specific leaf area and a high leaf weight ratio, and consequently a high leaf area ratio, whereas selection in nutrient-poor habitats has led to species with an inherently low specific leaf area and a higher fraction of root mass, and thus a low leaf area ratio.     

In vitro attempts to overcome the cross-incompatibility between Vaccinium corymbosum L. and V. elliottii Chapm.

Summary Seed was readily obtained from V. corymbosum zygotes using embryo rescue techniques, even when embryos were cultured at proembryonic stages. Best in vitro seed development was obtained when ovules were cultured attached to placental tissues. Successful fruit and seed development in culture occurred only when the fruit was cut longitudinally or when the basal portion of the fruit was removed previous to plating. Addition of various vitamins, amino acids, and growth regulators to the nutrient medium did not increase seed production. Attempts to rescue hybrid embryos from V. croymbosum (tetraploid) x V. elliottii (diploid) crosses by in ovulo and in ovary culture gave a few presumably hybrid seed, but at a rate no greater than when normal crossing procedures are used.Florida Agricultural Experiment Station Journal Series No. 5748     

Simultaneous selection for grain yield and protein percentage in backcross populations fromAvena sterilis ×A. sativa matings by using the independent culling levels procedure

Summary The method of independent culling levels was applied for simultaneous improvement in grain yield, protein percentage, and protein yield in a population of oat lines from the BC₀–BC₅ of the interspecific matingAvena sativa ×A. sterilis. Grain yield and protein percentage were subjected to selection with various combination of culling levels to give samples with 2% of the lines from the original population. — Intense selection for grain yield resulted in samples with high grain and protein yields but low protein percentage. Intense selection for protein percentage resulted in samples with high protein percentage but low grain and protein yields. The sample selected for protein yield only showed no significant difference from the recurrent parent for any trait. The recommended regime for improving protein percentage and grain and protein yields simultaneously was one that initially saved approximately 25–50% of the original population on the basis of protein percentage, and then provided intense selection for grain yield on the lines that remained. At least three backcrosses were necessary to obtain lines with high protein percentage and acceptable agronomic traits.Journal Paper No. J-11439 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project No. 2447     

The genomic relationships among six wild perennial species of the genus Glycine subgenus Glycine Willd.

Summary Based on meiotic chromosome behavior in intra- and interspecific hybrids, genome symbols were assigned to the following diploid (2n=40) Glycine species: G. canescens = AA; G. clandestina- Intermediate pod (Ip)=A ₁ A ₁; G. clandestina-Short pod (Sp)=BB; G. latifolia = B ₁ B ₁; G. tabacina = B ₂ B ₂; G. cyrtoloba = CC; and G. tomentella = DD. Genome symbol GG was reserved for the soybean, G. max. At metaphaseI, loose chromosome associations were observed in completely sterile interspecific hybrids whose parents differed in their genomes, suggesting some chromosome homologies among species. Although G. clandestina-Sp, G. latifolia and G. tabacina are morphologically distinct species, they differ only by a paracentric inversion. Similar observations were recorded for G. canescens and G. clandestina-Ip. Evidence is presented that demonstrates that G. tabacina (2n=80) and G. tomentella (2n=78, 80) are allotetraploid species complexes. Hybrid weakness, sterility, seedling lethality and seed inviability were found in intra- and interspecific hybrids.This research was supported in part by the Illinois Agricultural Experiment Station and the U.S. Department of Agriculture (Special grant 82-CRSR-2-2007). Travel grants to collect Glycine germplasm were received from the Rockefeller Foundation, the Illinois Soybean Program Operating Board, the National Science Foundation (INT76-14753) and the International Board for Plant Genetic Resources     

Mesoderm induction in the future tail region of Xenopus

Summary We have used interspecific grafts between Xenopus borealis and Xenopus laevis to study the signalling system that produces tail mesoderm. Early gastrula ectoderm grafted into the posterior neural plate region of neurulae responds to a mesodermal inducing signal in this region and forms mainly tail somites; this signal persists until at least the early tail bud stage. Ventral ectoderm grafted into the posterior neural plate loses its competence to respond to this signal after stage 10 1/2. We have established the specification of anterior and posterior neural plate ectoderm. In ectodermal sandwiches or when grafted into unusual positions, anterior regions gave rise to mainly nervous system and posterior regions to large amounts of muscle, together with some nervous system. Thus it was impossible to assess the competence of posterior neural plate ectoderm to form further mesoderm and hence to establish if mesodermal induction continues during neurulation in unmanipulated embryos.     

The ‘A’ genome donor of Eleusine coracana (L.) Gaertn. (Gramineae)

Summary In an attempt to discover A and B genome donor(s) to finger millet, Eleusine coracana, or its progenitor species, E. africana (both allotetraploid 2n=4x=36), five diploid species, E. Indica, E. Floccifolia, E. multiflora, E. tristachya and E. intermedia, were crossed to finger millet and its progenitor taxon. Crosses were successful only with E. coracana. Three combinations of triploid hybrids E. coracana x E. indica, E. coracana x E. floccifolia, and E. coracana x E. multiflora were obtained and analysed. Meiotic behaviour was perfectly normal in parental species. The regular number of 18 bivalents in E. coracana, 9 bivalents in E. indica, E. intermedia, E. tristachya and E. floccifolia and 8 bivalents in E. multiflora were invariably noticed. In E. coracana x E. indica hybrids a mean chromosome pairing of 8.84_I+8.80_II+0.03_III+0.10_IV per cell was found. About 86.5% of the cells showed the typical 9_I+9_II configuration, suggesting that E. indica (AA) is one of the diploid genome donors to cultivated species E. coracana. A mean chromosome pairing of 11.08_I+7.63_II+0.16_III+0.04_IV per cell was found in E. coracana x E. floccifolia hybrids. Two to ten bivalents and varying numbers of univalents were seen in 55% of the cells. About 45% of the cells showed the 9_I+9_II configuration. Various evidence suggests that perennial E. floccifolia is a primitive member of the A genome group of Eleusine species, and it may not be a genome donor to E. coracana. In E. coracana x E. multiflora hybrids (2n=26) mean chromosome pairing of 21.45_I+1.97_II+0.13_III+0.04_IV per cell was found. About 91% of the cells were observed to have 20–26 univalents. Only a small percentage of the cells contained bivalents or multivalents. This pairing behaviour indicates that E. multiflora lacks genomic homology with the A or B genome of E. coracana. Genomically E. multiflora is a distinct species and a genomic symbol of C is assigned to it. Identification of the B genome donor species to cultivated millet. E. coracana remains elusive.     

Transfer of bacterial blight and blast resistance from the tetraploid wild rice Oryza minuta to cultivated rice,Oryza sativa

Summary Oryza minuta J. S. Presl ex C. B. Presl is a tetraploid wild rice with resistance to several insects and diseases, including blast (caused by Pyricularia grisea) and bacterial blight (caused by Xanthomonas oryzae pv. oryzae). To transfer resistance from the wild species into the genome of cultivated rice (Oryza sativa L.), backcross progeny (BC₁, BC₂, and BC₃) were produced from interspecific hybrids of O. sativa cv IR31917-45-3-2 (2n=24, AA genome) and O. minuta Acc. 101141 (2n=48, BBCC genomes) by backcrossing to the O. sativa parent followed by embryo rescue. The chromosome numbers ranged from 44 to 47 in the BC₁ progeny and from 24 to 37 in the BC₂ progeny. All F₁ hybrids were resistant to both blast and bacterial blight. One BC₁ plant was moderately susceptible to blast while the rest were resistant. Thirteen of the 16 BC₂ progeny tested were resistant to blast; 1 blast-resistant BC₂, plant 75-1, had 24 chromosomes. A 3 resistant: 1 susceptible segregation ratio, consistent with the action of a major, dominant gene, was observed in the BC₂F₂ and BC₂F₃ generations. Five of the BC₁ plants tested were resistant to bacterial blight. Ten of the 21 BC₂ progeny tested were resistant to Philippine races 2, 3, and 6 of the bacterial blight pathogen. One resistant BC₂, plant 78-1, had 24 chromosomes. The segregation of reactions of the BC₂F₂, BC₂F₃, and BC₂F₄ progenies of plant 78-1 suggested that the same or closely linked gene(s) conferred resistance to races 2, 3, 5, and 6 of the bacterial blight pathogen from the Philippines.     

Where did Mikrotia magna originate? Drawing ecogeographical inferences from body mass reconstructions

Terre Rosse deposits (upper Miocene; Gargano, Italy) have provided fossil remains of an insular fauna among which the genus Mikrotia (Rodentia) stands out. Several paleobiological studies have already been conducted on this genus, but its body mass has not yet been calculated accurately. The aim of the present work is to reconstruct Mikrotia magna's weight, a paramount aspect of organismal biology, especially on islands where mammals modify their size, becoming giants or dwarfs (‘island rule’). Our analysis using postcranial elements (femora and humeri) predicts weights ranging from 1300 g to 1900 g (old and young populations, respectively). The presence of a large number of micromammals on the Gargano paleo-island suggests a high interspecific competition for species of the same ecological guild (Prolagus or cricetids were direct competitors of Mikrotia), which may lead to only moderate gigantism, or even body mass reductions in small mammals, following Palkovacs's model. This contrasts with the huge weight of M. magna inferred in this study. In this regard, stratigraphic and taxonomic studies suggest that M. magna was an immigrant from a neighboring island, indicating that this species originated and achieved its enormous size under other selective pressures. A native island with a lower number of competitors, and therefore with less resource limitation than Terre Rosse, might be the principal explanation for such a degree of gigantism.     

Cytological study of interspecific hybrid between Brassica campestris x B. hirta (Sinapis alba)

Interspecific hybrids from the crossing Brassica campestris x B. hirta are reported in our study for the first time. F₁ plants were obtained by using ovary culture. The phenotype of hybrids was similar to B. napus; the plants were self-fertile. Investigation of meiotic division and nuclear DNA content measurements showed the amphidiploid origin of these hybrids. The relationship between genome A and D, as well as the spontaneous amphidiploidization of the hybrids, are discussed.