Vernalization in Chickpea (Cicer arietinum); Fact or Artefact?

Various cool treatments of imbibing seeds reduced the subsequenttimes taken to flower in two genotypes of chickpea (Cicer arietinumL.). These reductions were greater in the kabuli cv. Rabat thanin the desi accession ICC 5810. Nevertheless, in both genotypes,the hastening of flowering was entirely accounted for by thephotothermal time accumulated during each cool temperature pretreatment,provided it was recognized that the ceiling photoperiods wereapproximately 10 and 8 h d^–1, respectively; i.e. neithergenotype shows a true vernalization response. A thorough reevaluationof ‘ responsiveness to vernalization’ in the chickpeagermplasm might now be prudent. Cicer arietinum L, chickpea, vernalization, photothermal time, screening germplasm     

Effects of barley mildew on green leaf area and grain yield in field and greenhouse experiments

In 1980 the relationships between mildew severity, green leaf area (GLA) and grain yield of spring barley were examined using greenhouse-grown plants and plants grown in micro-plots in the field. Mildew, by causing premature senescence, reduced GLA and grain yield was strongly correlated with GLA integrated from growth stages 2–10.5 on the Feekes scale. Early mildew attack reduced all yield components (including grain size) even when fungicidal control had eliminated mildew by anthesis. Analyses of culms at anthesis and harvest supported the view that the smaller grain size associated with early mildew attack resulted from a deficiency in carbohydrate stored in culms before anthesis and available for retranslocation to the developing grain. Amounts of total soluble carbohydrate at anthesis and the amounts lost beween anthesis and harvest were both strongly correlated with GLA up to anthesis.     

Culicoides aspirated from cattle in Costa Rica, Honduras, Panama and Puerto Rico, and their role as potential vectors of bluetongue viruses

Abstract. In 1991, as part of an epidemiological study of bluetongue viruses (BTV) in the Central American and Caribbean region, eight farms located in Costa Rica, Honduras, Panama and Puerto Rico were sampled for Culicoides spp. attacking cattle. Using cattle bait, 3884 biting midges were collected with an electric aspirator during both crepuscular periods. The predominant species captured was Culicoides insignis Lutz (95%), followed by C.furens (Poey) (3.4%), C.filarifer Hoffman/ C.ocumarensis Ortiz (0.9%), C.lahillei (Iches) (0.7%), C.arubae Fox and Hoffman (<0.1%) and C.gorgasi Wirth and Blanton (<0.1%). Blood-engorged specimens from some of these species were collected and comprised: 18% of all C.insignis , 36% of C.furens , 37% of filarifer/ocumarensis and 25% of C.lahillei. No engorged C.arubae or C.gorgasi were caught. These results confirm earlier findings pointing to C.insignis, C.furens and C.filarifer/ ocumarensis as potential vectors of BTV in the region.     

Asymptotes of diseases caused by non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars

A model describing disease progress of non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars (Jeger, Griffiths & Jones, 1981b) has been extended beyond the logarithmic phase of disease development. The extended. logistic model indicates that whatever the outcome in the early stages (disease less than or more than the mean of disease in the pure stands), disease will eventually level off at a value equal to the mean of disease asymptotes in the pure stands. The time scale involved in such levelling-off, however, means that substantial benefit may still be expected from deployment of such mixtures. Analytical solutions for the model are obtained for the special case where the ratio of disease asymptote to initial disease is the same for each pure stand.     

Irrigation and Seed Quality Development in Rapid-cycling Brassica: Seed Germination and Longevity

Irrigation of rapid-cycling brassica (Brassica campestris [rapa]L.)plants either ended 16 or 24 days after pollination (DAP) orcontinued throughout the experiment (control). Seeds were harvestedserially from these plants during their development and maturation.The earlier irrigation to the mother plant ended, the earliermass maturity (end of seed-filling phase) occurred, the lowerthe final seed dry weight, and the more rapid the decline inseed moisture content. The onset of ability to germinate normallyoccurred as early as 12 DAP, when seeds were less than half-filled.The onset of ability to tolerate rapid enforced desiccation(to 10% moisture content) occurred at 16 DAP. Desiccation tolerancedeveloped within most seeds in both populations about 5 d soonerin seeds harvested from plants in which irrigation was stoppedat 16 DAP than in control plants, but maximum desiccation toleranceoccurred at about 28 DAP in all treatments. Survival curves(percentage normal germinationvs.period of storage) of seedshermetically stored at 40 °C with 15% moisture content conformedto negative cumulative normal distributions, and provided acommon estimate of the standard deviation of the frequency distributionof seed deaths in time for seed lots harvested at differenttimes from the three environments (     

Yield in spring barley at contrasting sites in England and Scotland

The yield and yield components of tall and short genotypes derived from the cross between two spring barley cultivars, Ark Royal and Golden Promise were examined. The genotypes were grown at two locations in England and two in Scotland. The highest yields were observed at two English sites (in East Anglia) rather than, as expected, in Scotland (East Lothian). Higher yield at the English sites was related to the greater means recorded for all the components of yield. The tall genotypes produced higher yields than the short genotypes, particularly at sites affected by drought. There were significant interactions between genotypes and environments for plot yield. Selection for increased yield would have been possible within either tall or short lines.