Utilization of plant genetic resources in crop breeding programmes

There are a wide variety of ways in which plant genetic resources are used in crop breeding programmes. These depend upon the problems which the breeder is t&g to solve, the resources at hand to solve them, the reproductive biology of the crop, and the availability of appropriate genetic resources collections. The important fact is that all breeding programmes depend on genetic resources of one type or another to make progress in improving yield, disease or pest resistance, and produd quality of the crop, forage or ornamental plants they are responsible for. This paper considers in general terms some of the important ways in which genetic resources collections are used in m&k plant breeding programmes, and illustrates the general principles with an example of different uses of a very good national genetic resources collection in a breeding programme currently in its initial stages in Namibia

Field screening for drought tolerance - principles and illustrations

Establishing a screening procedure for genetic differences in drought tolerance involves 1) practical decisions on the objectives of such a screening program, 2) the selection of environment(s) and stress occurrence(s) to be targeted in the program, and 3) the design and operation of field physical facilities and experimental methods to apply a uniform, repeatable drought stress. This paper considers these points from a conceptual and a practical viewpoint. Drought tolerance can be approached on various plant organizational levels, from crop yield stability under stress, through responses to stress indicative of tolerance, to the biological mechanisms that underlie these responses, to the genes and alleles governing the presence or expression of the responses/mechanisms. Defining stress tolerance at each level has specific advantages and disadvantages for designing a field-screening program. Work on pearl millet has mainly focused on the crop tolerance response level, targeting the relative ability of genotypes to maintain grain numbers per panicle and seed filling in terminal stress environments. Target environments and target stress occurrences for a screening program must be established from the analysis of historical climate data. Water budgeting is probably the minimum level, but opportunities to use crop simulation modeling for this purpose are improving. Establishing screening systems with environmental conditions representative of the target environment, is difficult, involving a major tradeoff between providing representative daylength, vapor pressure, and temperature conditions, and easily managing soil water/rainfall. In contrast, duplicating target environment moisture patterns in non-target environments is easier, but G x E effects can be a problem. The effectiveness of a drought screening procedure is best measured by the genetic heritabilities achieved for target traits, whether the focus is nurseries therefore requires careful analysis of likely sources of nongenetic variation among plots, replications, and repeated experiments, and seeing that these are minimized. These include 1) the choice of site for screening, 2) the physical management of both water-related and non water-related sources of variation in crop growth within and across experiments, 3) the choice of experimental design and the effective use of blocking to remove expected sources of nonmanageable variation, and 4) the efficient collection and management of data. These considerations are illustrated here with examples from the pearl millet drought screening system used at ICRISAT

Water stress and time of floral initiation in pearl millet

The interaction of water stress and time from sowing to floral initiation was investigated in the field with pearl millet hybrid BJ 104. Extended daylength was used to delay panicle initiation (PI) and flowering (FL) of crops exposed to single periods of mid-season drought. Growth, yield and yield components were related to the number of days for PI and FL in both irrigated and water-stressed treatments. Delay in PI resulted in more leaves and tillers per plant, and greater leaf area, height and total dry matter. Grain yield, however, was not affected resulting in lower ‘harvest index’. There was, however, an increase in the grain yield of main shoots which was offset by a proportional decrease in the grain yield of tillers. Water stress effects were dependent on the physiological stage of the crop at which stress occurred, as a result of the photoperiod treatments. Water stress prior to panicle initiation did not affect the grain yield of the main shoot but increased tiller grain yield, resulting in a higher total (crop) grain yield. Water stress during panicle development reduced the grain yield on the main shoot but this loss was compensated by the grain from the increased number of tiller panicles which reached flowering. Water stress during flowering and grain filling reduced grain yields of both main shoot and tillers, making this the most sensitive stage. Photoperiodic control of floral initiation can provide an escape mechanism to avoid the coincidence of mid-season water stress with sensitive periods of growth

Drought Research Priorities for the Dryland Tropics

This book is the product of a consultants' meeting held at the International Crops Researech Institute for the Semi-Arid Tropics in Patancheru, India, on 17-20 Nov 1986. The meeting brought together specialists from a number of disciplines to discuss priorities for applied research on improving crop production in the arid and semi-arid tropics. The invitees were asked to focus on research topics with a high degree of promise for the short to medium term, with a particular emphasis on the application of existing knowledge or technology to the problems of the dry tropics. The meeting was organized into four separate sessions, which have been retained as the four parts of this book. Parts 1 and 2 deal with more effective means of analyzing the climate of dry environments and of selecting technologies to f i t the expected moisture patterns. Part 1 considers methodologies for using climate data in conjunction with soil, atmospheric, and crop data to provide a quantitative picture of crop-available moisture in dry environments. Part 2 looks at the basis of, and at methods for, fitting crops, crop and soil management systems, and crop varieties to the specific environments in which they are the most productive and/or provide the greatest stability of production

Water deficit during panicle development in pearl millet: yield compensation by tillers

Water deficit during the panicle development stage reduced the grain yield of the main shoot panicle of pearl millet but this loss was compensated by increased grain yield of the tillers. The potential extent of compensation in grain yield components by tillers was investigated by removing the main shoot at panicle initiation (PI) and flowering stages respectively, for both irrigated and water-stressed plants. Grain yield loss by removal of the main shoot of plants at PI was fully compensated by tiller grain yield in both the irrigated and water-stressed plants. The compensation was, however, only partial when the main shoot was removed at flowering. The compensation for the grain yield loss in the main shoot due to either water stress or removal was through an increase in number of grains on the tillers. This increase was due to an increase in the number of productive tillers in the case of water stress and to both an increase in the number of productive tillers and an increase in the number of grains per panicle in the case of main shoot removal. This compensatory mechanism by tillers plays an important role in overcoming the effects of pre-flowering water stress damage to the main shoot

Effect of the duration of the vegetative phase on crop growth, development and yield in two contrasting pearl millet hybrids

The phenotype of medium duration pearl millet varieties grown in West Africa differs from that of the shorter duration millets grown in India. African varieties are usually much taller, have longer panicles, fewer productive tillers, and a lower ratio of grain to above-ground dry-matter (harvest index). The effect of crop duration on plant phenotype was investigated in two hybrids using extended daylengths to increase the duration of the vegetative phase (GSl: sowing to panicle initiation). The two hybrids, 841A × J104 and 81A × Souna B, were considered to represent the Indian and African phenotype, respectively. Tiller production and survival, leaf area, and dry-matter accumulation and partition, were monitored over the season. Grain yield and its components were determined at maturity. The two hybrids responded similarly to the short and long daylength treatments. The duration of GSl was increased from 20 to 30 days, resulting in increased number of leaves, leaf area, and stem and total dry-matter accumulation; there was no effect on tiller production and survival, or on panicle growth rate. Grain yield was, therefore, the same in both GSl treatments, and harvest index (HI) was much reduced in the long GSl treatment owing to the increased stem growth. One evident effect of a longer GSl was on dry-matter partitioning between shoots; partitioning to the main stem (MS) was increased, whereas partitioning to the tillers was reduced. There was no difference in crop development, growth or yield between the two hybrids in either GSl treatment. The only significant differences were in the efficiency with which intercepted radiation was converted to dry matter, which was greater in 841A × J104 than in 81A × Souna B, and in the balance between MS and tillers; the grain yield of the MS was significantly greater in 81A x Souna B than in 841A × J104, but at the expense of number of productive tillers. The results demonstrate that both African and Indian phenotypes are equally productive under good agronomic conditions. The lower HI in longer duration African millets is a consequence of a much extended stem growth phase and therefore increased competition between stem and panicle during grain filling. Possible ways to increase grain yield in the medium duration African millets are considered

Determinants of ruminant nutritional quality of pearl millet [Pennisetum glaucum (L.) R.Br.] stover: I. Effects of management alternatives on stover quality and productivity

The paper investigates management and cultivar type effects on pearl millet stover yield and fodder quality. Sixteen pearl millet cultivars available to farmers in India were selected to represent three cultivar types: (1) traditional landrace germplasm from the arid/semi-arid millet production zones, (2) improved dual-purpose (grain and stover) open-pollinated varieties incorporating differing amounts of traditional landrace germplasm and (3) commercial, grain-type F1 hybrids, bred for use in the arid/semi-arid zone. The cultivars were grown for 2 years (2000 and 2001) at high fertility (HF: 65 kg N ha-1 and 18 kg P ha-1) and low fertility (LF: 21 kg N ha-1 and 9 kg P ha-1). Within each fertility level high (HP) and low (LP) plant population densities were established by varying sowing rate and then thinning to the target populations (HP: 11 plants m-2 and LP: 5 plants m-2). Stover fodder quality traits (nitrogen concentration, sugar content, in vitro digestibility and metabolizable energy content) were analyzed using a combination of conventional laboratory analysis and near infrared spectroscopy. In general, fertility level and cultivar type had strong effects on grain and stover yields, and on a range of stover nutritional quality traits, but with significant year interactions. In contrast, the effect of population density on these variables was largely insignificant. Higher fertilizer application significantly increased grain and stover yields and stover nitrogen concentration, in vitro digestibility and metabolizable energy content. As a result, fertilization resulted in significant increases in the yields of both digestible and metabolizable stover. Landrace cultivars as a group produced higher quality fodder than modern hybrids, but at a significant cost in grain yield. Dual-purpose, open-pollinated cultivars were generally intermediate between the landraces and hybrids, in terms of both stover quality and grain yield, but produced the highest yields of both digestible and metabolizable stover. The paper discusses the implications of these findings for Indian pearl millet farmers with various resource levels and farming objectives

The influence of extended vegetative development and d2 dwarfing gene in increasing grain number per panicle and grain yield in pearl millet

As in other cereals, grain yield in pearl millet is directly related to grain number m−2. Hence, an attempt was made to increase grain numbers by (1) increasing the length of vegetative period (to increase potential grain number per panicle and increase leaf area and light interception before flowering) by using a non-inductive long photoperiod during the early stages of crop growth, and (2) using a dwarfing gene to vary assimilate partitioning between panicle and stem prior to flowering. Extended day length delayed panicle initiation (PI) and flowering and increased leaf area index and assimilate production. Time to flowering was directly related to assimilate allocation to individual panicles, and to grain number per panicle. Delayed PI, however, reduced panicle numbers. Dwarf hybrids partitioned more assimilates to panicles and less to stems, which was also associated with more grains per panicle. The increase in grain number per panicle was offset by decrease in panicles per plant so that neither longer vegetative stage nor dwarfing gene caused in increase in grain yield. With increase in grain numbers per panicle in the dwarfs, grain density (grains cm−2 surface area of panicle) also increased resulting in the dwarf hybrids producing smaller grains and failing to benefit from the increased grain numbers per ear

Genotypic variation in biomass production and nitrogen use efficiency in pearl millet [Pennisetum americanum (L.) Leeke]

Twenty diverse pearl millet genotypes ranging from landraces to high yielding hybrids were studied for genotypic variation in nitrogen (N) use efficiency in high (100 kg N/ha) and low fertility (20 kg N/ha) over two years in the field. The combined data over years and fertility levels indicated that despite taking up similar amounts of N, genotypes differed significantly in biomass production and thus in N use efficiency. A West African genotype, Souna B, had N use efficiency values 32% higher than the less efficient Indian genotype BJ 104 even though both genotypes had similar N uptake. An increase in N fertility decreased N use efficiency since the percentage increase in biomass was smaller than the percentage increase in N uptake