Development of male-specific markers and identification of sex reversal mutants in papaya

Papaya is a productive and nutritious fruit grown in tropical and sub-tropical regions worldwide. It is polygamous with three sex types: female, male and hermaphrodite. Sex determination in papaya is controlled by an XY sex chromosome system with two slightly different Y chromosomes, Y for males and Y^h for hermaphrodites. Comparative analysis of the hermaphrodite-specific region of Y^h chromosome (HSY) and male-specific region of Y chromosome (MSY) revealed 99.6% sequence identity, which explains why DNA markers that amplify for both males and hermaphrodites have easily been developed, but not for the male trait specifically. We examined the 0.4% sequence differences, and found 1887 indels and 21,088 SNPs between MSY and HSY. The vast majority of indels are single nucleotide or few base pairs. A large male-specific retrotransposon insertion of 8396 bp was used to develop two papaya male-specific markers, PMSM1 and PMSM2 that amplify 585 and 548 bp fragments, respectively. These two markers were tested in 11 gynodioecious and four dioecious varieties along with autosomal DNA marker 71E and male/hermaphrodite marker W11, and the results showed clear separation of male from hermaphrodite and female. PMSM1 and PMSM2 were also used to test the sex type of six sex male-to-hermaphrodite reversal mutants which are crucial materials for validating candidate genes for sex determination in papaya. Our result showed all six mutants were positive for the male-specific markers. These male-specific markers can be used to distinguish gynodioecious and dioecious cultivars in papaya seed market, and facilitate genetic and genomic research for papaya improvement.     

Indices of soil nitrogen availability for an ecological site classification of British forests

An adequate supply of nitrogen (N) is essential for the successful establishment and sustainable productivity of forest stands. N deficits may necessitate the use of artificial fertilisers. Availability of N in the inorganic forms, and the relative abundance of the NO₃-N and NH₄-N components, influences the species composition of natural forest vegetation. Hence it is essential to use reliable measures of soil N supply that fully reflect its ecological significance. The new Ecological Site Classification (ESC) used in British forestry employs a multi-factorial definition of soil nutrient regime (SNR), including soil N. To develop this, a soil and vegetation study was made at 89 forest sites throughout Great Britain covering the major soil types used for forestry. “Total N” levels were compared with separate pre- and post-incubation measures of the two inorganic N components as potential indices of soil N supply. Multivariate statistical analysis showed that the major discriminant chemical variables for the sampled soils were pH, calcium and NO₃-N and that these were also the main variables influencing the species composition of the ground vegetation. Total N and NH₄-N were less effective discriminant variables for these sites. In some infertile soils the levels of NH₄-N or total N may be of greater importance, as NO₃-N is usually in very limited supply. A multivariate gradient of SNR, which incorporates the NO₃-N measures, has been adopted for use within the ESC system. The position of a site on this gradient can be estimated quantitatively from soil type, ground vegetation species composition and humus type. This enables soil N supply and overall SNR to be assessed in a simple but effective way that guides the operational management of British forest soils for sustainable productivity. It will also be possible to use these techniques to monitor the nutritional status of forest sites over time.     

Frequency and fertility restoration efficiency of Rf3 and Rf4 genes in Indian rice

Identification of new parental lines is crucial for developing ecology‐specific hybrids with ideal agronomic performance. We screened a total of 570 different ecology‐specific Indian rice varieties for the presence of fertility restorer genes, Rf3 and Rf4 using tightly linked markers DRRM Rf3‐10 and RM6100, respectively. Among these varieties, 13% carried Rf3Rf3/Rf4Rf4, 31% carried rf3rf3/rf4rf4, 6% carried Rf3Rf3/rf4rf4 and remaining 50% carried Rf4Rf4/rf3rf3 allelic combinations. A mini set of 40 varieties with variable allelic combinations of fertility restorer genes were testcrossed with WA and Kalinga‐based CMS lines. All the 80 F₁s were evaluated for spikelet fertility and fertility restoration ability. Rf3Rf3/rf4rf4 genotypes mostly behaved as partial maintainers or partial restorers. In contrast, rf3rf3/Rf4Rf4 genotypes were partial or effective restorers. However, double dominant genotypes showed better fertility restoration than the genotypes containing Rf3 or Rf4 individually. Some of the genotypes showed unexpected restoration pattern implying occurrence of other fertility restorer(s) apart from Rf3 and Rf4. The perfect restorers and maintainers identified in this study can be directly used in hybrid rice breeding.     

Effect of plastic mulch on water flow and herbicide transport in soil cultivated with pineapple crop: A modeling study

In Hawaii, pineapple is typically grown in raised beds covered with impervious plastic mulch. Field measurements of a commonly used herbicide (bromacil) mass beneath mulch-covered pineapple beds and inter-bed open areas revealed that open areas contained a mass of bromacil about 3.5 times greater than was originally applied, based on label instructions, to the entire field. The broadcast bromacil ended up in the inter-bed open areas through water runoff from the plastic mulch covering the pineapple beds. The objective of this study was to evaluate the impact of surficial management on water dynamics and bromacil concentration in the soil on a pineapple plantation using the one- (1D) and two-dimensional (2D) flow and transport models. Flow and transport processes were simulated in a 2D vertical cross-section perpendicular to the plant rows. The 1D simulation was limited to the open inter-bed areas. Several simulation scenarios were proposed to evaluate the effect of plastic mulch on bromacil transport in soil. In our simplified approach, the water and solute boundary fluxes for the non-covered areas were increased to simulate the water and solute contribution from the plastic mulch surface. The simulation results were compared with field observations of soil water potentials and resident bromacil concentration profiles. The field and laboratory-measured hydraulic and transport parameters were used for all simulation scenarios. Reasonably good agreement between the model-predicted and observed soil water potentials and bromacil concentration profiles was obtained. Biased 1D and 2D results were predicted when the water runoff from plastic mulch was neglected. The 1D approach to quantify bromacil transport beneath the inter-bed open areas seemed to be sufficient in case the water runoff from the mulch was taken into account.     

Evaluating evaporation from field crops using airborne radiometry and ground-based meteorological data

Summary Airborne measurements of reflected solar and emitted thermal radiation were combined with ground-based measurements of incoming solar radiation, air temperature, windspeed, and vapor pressure to calculate instantaneous evaporation (LE) rates using a form of the Penman equation. Estimates of evaporation over cotton, wheat, and alfalfa fields were obtained on 5 days during a one-year period. A Bowen ratio apparatus, employed simultaneously, provided ground-based measurements of evaporation. Comparison of the airborne and ground techniques showed good agreement, with the greatest difference being about 12% for the instantaneous values. Estimates of daily (24 h) evaporation were made from the instantaneous data. On three of the five days, the difference between the two techniques was less than 8%, with the greatest difference being 25%. The results demonstrate that airborne remote sensing techniques can be used to obtain spatially distributed values of evaporation over agricultural fields.     

Cell wall polysaccharides from chalkumra (Benincasa hispida) fruit. Part I. Isolation and characterization of pectins

Pectic polysaccharides were obtained from chalkumra (Benincasa hispida) fruit by sequential extraction with ammonium oxalate (fraction BOX), dilute acid (fraction BHCl), and cold dilute alkali (fraction BOH). The highest yield of polysaccharides was obtained with oxalate and HCl. BOX was enriched in partly methyl-esterified galacturonic acid, whereas BHCl and BOH contained mostly galactose. All of the extracts showed similar elution patterns in size exclusion chromatography although the intrinsic viscosities (eta) were different (132 +/- 6, 100 +/- 5, and 285 + 10 mL/g for BOX, BHCl, and BOH, respectively). From fractionation by anion exchange chromatography, homogalacturonan (as seen from sugar analysis and Fourier transform infrared spectrum) accounted for more than half of BOX and 11% of BHCl. Methylation analyses and hydrolysis of BHCl with endo-beta-(1-->4)-d-galactanase showed the presence of beta-(1-->4)-d-galactan. The neutral galactan represented more than 76% of BHCl and approximately 40% of BOH. The other polysaccharides were complex galactans in BOH and an acidic arabinan (<1%) in BOX and BHCl.     

Increasing Returns to Scale in Affluent Knowledge‐Rich Economies

This paper departs from the existing growth literature in not assuming a priori a specific production technology and offering instead a theory of production technology that captures the effects of changes in the level, composition, and forces of accumulation of capital on the productivity of an economy. The theory of production technology shows that an affluent knowledge‐rich economy violates the Inada second condition because of its high level of knowledge, human, and social capital. Substitution of knowledge capital for physical capital and the self‐reinforcing nature of the process of accumulation of knowledge, human, and social capital are the engines of growth in such economies. Poor economies, on the other hand, may exhibit neoclassical production technology of diminishing returns to capital and get trapped into a low‐level steady state owing to their ever‐growing need for physical capital and also to unfavorable supply conditions for knowledge capital, lower levels of knowledge, human, and social capital in these economies being inadequate to trigger the self‐reinforcing dynamics. The mechanics of endogenous growth are essentially different in rich and poor economies because the production possibility surface is non‐convex in the former, and this difference explains the sustained divergence of their growth rates.     

Relationship of morphological variables to rubber production in guayule

Summary The objective of this study was to find measurable characters to aid the plant breeder in predicting both rubber percentage and rubber yield of guayule (Parthenium argentatum Gray). A field of 234 guayule breeding lines was harvested by clipping in February 1986. Forty-two of these lines were selected for further evaluation on the basis of superior regrowth, rubber content and yield. These 42 lines were reharvested in February 1987. Nineteen variables were evaluated including percent rubber and resin, rubber and resin yield (g/plant), plant height (cm), width (cm), and volume (m³), fresh and dry weight (kg/plant), percent dry weight, stem number, mean stem diameter (cm), total and mean stem circumference (cm), total and mean stem area (cm²), total stem circumference/total stem area (cm^-1), and regeneration at two dates. Dry weight (kg/plant) had the best correlation to rubber yield (r=0.85), and plant volume best predicted dry weight (r=0.83). These variables did not correlate as highly with percent rubber. The best statistical regression model for percent rubber included four variables, fresh and dry weight, percent dry weight, and plant volume. This model accounted for 51% of the variation. In comparison, the best regression of rubber yield had an R²=0.85 for plant height and width, volume, and dry weight.     

Modeling carbon allocation in trees: a search for principles

We review approaches to predicting carbon and nitrogen allocation in forest models in terms of their underlying assumptions and their resulting strengths and limitations. Empirical and allometric methods are easily developed and computationally efficient, but lack the power of evolution-based approaches to explain and predict multifaceted effects of environmental variability and climate change. In evolution-based methods, allocation is usually determined by maximization of a fitness proxy, either in a fixed environment, which we call optimal response (OR) models, or including the feedback of an individual's strategy on its environment (game-theoretical optimization, GTO). Optimal response models can predict allocation in single trees and stands when there is significant competition only for one resource. Game-theoretical optimization can be used to account for additional dimensions of competition, e.g., when strong root competition boosts root allocation at the expense of wood production. However, we demonstrate that an OR model predicts similar allocation to a GTO model under the root-competitive conditions reported in free-air carbon dioxide enrichment (FACE) experiments. The most evolutionarily realistic approach is adaptive dynamics (AD) where the allocation strategy arises from eco-evolutionary dynamics of populations instead of a fitness proxy. We also discuss emerging entropy-based approaches that offer an alternative thermodynamic perspective on allocation, in which fitness proxies are replaced by entropy or entropy production. To help develop allocation models further, the value of wide-ranging datasets, such as FLUXNET, could be greatly enhanced by ancillary measurements of driving variables, such as water and soil nitrogen availability.