Effects of Grain Development and Thermal History on Grain Maturation and Seed Vigour of Pennisetum americanum

Studies were made of the viability and vigour of seeds of pearlmillet (Pennisetum americanum) harvested at different stagesof grain development and from different controlled-temperatureenvironments. Seed viability and vigour of the next generationwere dependent on the extent of grain development at harvest.Where grain had developed for only one-third of the potentialgrain-filling period before harvest, seed viability and vigourwere greatly reduced. Harvest at or after the middle of grain-fillingdid not reduce seed viability or vigour. The temperature atwhich the grains had developed did not affect seed viability,but grains that had developed at 21/16 °C (day/night) producedseedlings of greater height and dry weight than those from grainswhich had developed at higher temperatures.     

Temperature and the pollinating activity of social bees

Abstract.

• 1 Thermal constraints on flight acivity limit the pollinating effectiveness of bees. Each species of social bee has a microclimatic ‘window’ within which foraging flight can be sustained.
• 2 To predict whether a given species of social bee is worth testing as a pollinator in a given climate, it is useful to know at least the lower limits of that microclimatic ‘window’. We consider how information from a series of bee counts through a day can be used to characterize a bee species in terms of activity/microclimate relations as a basis for predicting the diel pattern of foraging activity of a bee introduced into a new climate as a pollinator.
• 3 We discuss the relative merits of bee counts at a foraging patch and counts based on hive traffic as indices of the proportion of bees active.
• 4 We suggest that the activity/microclimate relations of a species be expressed in terms of the lower threshold black globe temperature for flight activity. Black globe temperature, T_g, is easily measured with inexpensive equipment, and can substitute for measurements of ambient temperature and radiation as a predictor of diel patterns of bee activity.
• 5 We use examples of field data to explore the relationship between microclimate and activity for the honeybee Apis mellifera and several species of bumblebee, Bombus. Regression analysis is used to relate activity to T_g and to identify the lower temperature threshold for activity from field bee counts.
• 6 In field studies analysed here, the bumblebees Bombus terrestrisllucorum, B.pascuorum and B.hortorum began foraging at lower temperatures than honey-bees or B.lapidarius.

     

Effect of Temperature During Various Growth Stages on Grain Development and Yield of Pennisetum americanum

In controlled temperature glasshouses plant morphology, gramdevelopment and yield of pearl millet (Pennisetum americanum)were markedly affected by temperature during three stages ofplant growth: vegetative, stem elongation, and grain development.High temperature (to 33/28 °C day/night) during all threegrowth stages lowered grain yields by reducing basal tillering,numbers of grains per inflorescence, and single grain weight.Low temperature (21/16 °C) during the vegetative stage increasedbasal tillering and, as a result, total grain yield per plant.However, low temperature during the stem elongation stage reducedspikelet fertility and influorescence length, and thereby reducedthe potential main shoot grain yield. Low temperature duringgrain development increased the grain filling period and grainyield. The rate of grain filling did not vary over the rangeof 21/16 to 33/28 °C. Although plant morphology and grainyield were markedly affected by pre-anthesis thermal environment,grain development was not. At all temperatures ethanol-solublecarbohydrates stored in the stem were depleted during earlygrain development.     

Structural Changes of the Grain Associated with Black Region Formation in Pennisetum americanum

The structure and ontogeny of grains of Pennisetum americanumare described with particular reference to the black regionon the abgerminal surface of the grain. Darkly pigmented materialwas deposited in the cells of the chalazal pad at black regiondevelopment. This colour development was associated with thecrushing of the transfer cells of the basal endosperm by theembryo and the cessation of transfer of ¹⁴C-labelled assimilateinto the grain. It is proposed that the growth of the embryointo the basal endosperm transfer cells and the subsequent accumulationof the pigmented material are the mechanisms by which graingrowth is halted.