Does maintaining green leaf area in sorghum improve yield under drought? II. Dry matter production and yield

Retention of green leaf area at maturity (GLAM), known as stay-green, is used as an indicator of postanthesis drought resistance in sorghum [Sorghum bicolor (L.) Moench] breeding programs in the USA and Australia. The critical issue is whether maintaining green leaves under postanthesis drought increases grain yield in stay-green compared with senescent hybrids. Field studies were undertaken in northeastern Australia on a cracking and self-mulching gray clay. Nine closely related hybrids varying in rate of leaf senescence were grown under two water-limiting regimes, post-flowering water deficit and terminal (pre- and postflowering) water deficit, and a fully irrigated control. Under terminal water deficit, grain yield was correlated positively with GLAM (r = 0.75**) and negatively with rate of leaf senescence (r = -0.74**). Grain yield also increased by ≃0.35 Mg ha-1 for every day that onset of leaf senescence was delayed beyond 76 DAE in the water-limited treatments. Stay-green hybrids produced 47% more postanthesis biomass than their senescent counterparts (920 vs. 624 g m-2) under the terminal water deficit regime. No differences in grain yield were found among eight of the nine hybrids under fully irrigated conditions, suggesting that the stay-green trait did not constrain yield in the well-watered control. The results indicate that sorghum hybrids possessing the stay-green trait have a significant yield advantage under postanthesis drought compared with hybrids not possessing this trait

Trends in Numbers and Changes in the Distribution of Feral Goats (Capra Hircus) in the South Australian Pastoral Zone

Trends in numbers and changes in the distribution of feral goats in the South Australian pastoral zone (217,300 km2) during 1978-94 were determined by winter aerial surveys. Only the presence or absence of goats on sample units was scored between 1978 and 1988. On the assumption of a random distribution of goat groups, these indices were transformed to densities of goat groups. Between 1989 and 1994 actual goat numbers were recorded on each sample unit, allowing goat density to be estimated. Goats were consistently at their highest densities in the south-east of the pastoral zone, a region dominated by open mallee scrub and chenopod shrubland. Densities of goat groups fluctuated from a low in 1984, following a drought, to a peak in 1990, following above-average rainfalls, when there were an estimated 193,700 - 29,600 goats in the pastoral zone. This estimate is conservative because it is uncorrected for the visibility bias associated with sighting groups and undercounting their sizes. The estimate also excludes the Flinders Ranges for which a similar number of goats has been estimated

The Prehistory of Potyviruses: Their Initial Radiation Was during the Dawn of Agriculture

Background: Potyviruses are found world wide, are spread by probing aphids and cause considerable crop damage. Potyvirus is one of the two largest plant virus genera and contains about 15% of all named plant virus species. When and why did the potyviruses become so numerous? Here we answer the first question and discuss the other. Methods and Findings: We have inferred the phylogenies of the partial coat protein gene sequences of about 50 potyviruses, and studied in detail the phylogenies of some using various methods and evolutionary models. Their phylogenies have been calibrated using historical isolation and outbreak events: the plum pox virus epidemic which swept through Europe in the 20th century, incursions of potyviruses into Australia after agriculture was established by European colonists, the likely transport of cowpea aphid-borne mosaic virus in cowpea seed from Africa to the Americas with the 16th century slave trade and the similar transport of papaya ringspot virus from India to the Americas. Conclusions/Significance: Our studies indicate that the partial coat protein genes of potyviruses have an evolutionary rate of about 1.1561024 nucleotide substitutions/site/year, and the initial radiation of the potyviruses occurred only about 6,600 years ago, and hence coincided with the dawn of agriculture. We discuss the ways in which agriculture may have triggered the prehistoric emergence of potyviruses and fostered their speciation

Farmer Participatory Early-Generation Yield Testing of Sorghum in West Africa: Possibilities to Optimize Genetic Gains for Yield in Farmers’ Fields

The effectiveness of on-farm and/or on-station early generation yield testing was examined to maximize the genetic gains for sorghum yield under smallholder famer production conditions in West Africa. On-farm first-stage yield trials (augmented design, 150 genotypes with subsets of 50 genotypes tested per farmer) and second-stage yield trials (replicated α-lattice design, 21 test genotypes) were conducted, as well as on-station α-lattice first- and second-stage trials under contrasting phosphorous conditions. On-farm testing was effective, with yield showing significant genetic variance and acceptable heritabilities (0.56 in first- and 0.61 to 0.83 in second-stage trials). Predicted genetic gains from on-station yield trials were always less than from direct testing on-farm, although on-station trials under low-phosphorus and combined over multiple environments improved selection efficiencies. Modeling alternative designs for on-farm yield testing (augmented, farmer-as-incomplete-block, multiple lattice, and augmented p-rep) indicated that acceptable heritabilities (0.57 to 0.65) could be obtained with all designs for testing 150 progenies in 20 trials and 75 plots per farmer. Ease of implementation and risk of errors would thus be key criteria for choice of design. Integrating results from on-station and on-farm yield testing appeared beneficial as progenies selected both by on-farm and on-station first-stage trials showed higher on-farm yields in second-stage testing