Showing papers on "Plant breeding published in 1977"

The importance of wild germplasm in plant breeding

Abstract: During the last few decades a considerable amount of work has centred round the importance of wild species in plant breeding . The interest in wild species and primitive cultivars has been strengthened through FAO's pioneer work on genetic resources of crop plants, as well as by the considerable efforts of Eucarpia in promoting gene bank activities in Europe over the last ten to fifteen years . It is also due in no small measure to breeders' clear nedds for a wider genetic base to help solve problems of resistance to disease, a greater range of environmental adaptation, better yields and better nutritional and economic characters in the plants concerned . In this paper I shall limit my remarks to the use of wild species, though much useful variation has been found in primitive cultivars also . Nevertheless the field is already so large, spreading into so many crops, that in a short review paper I shall be able to discuss only a limited range of examples . It may well be asked : why use wild species when so much diversity exists in the crops themselves? The answer is a pragmatic one, based on the nature of the crop in question . Thus, for crops such as field beans (Vicia faba) and cassava, apparently all the variation occurs in the crop itself . For others, such as barley and maize, certainly most of the useful variation exists in the crop . The wild prototypes, Hordeum spontaneum and Zea mexicana, seem to possess little of interest to the breeder, and species less related, such as other Hordeum species and Tripsacum species, need a great deal of preliminary manipulation before gene transfer can be effected . However, although this was once an obstacle, work of this nature is regarded as a problem which geneticists, biochemists and physiologists are now jointly trying to solve . For most crops a very wide gene pool exists in the wild species, as in potatoes for instance, from which transfers to the cultigens are quite feasible ; most species are cross compatible even though partial barriers are naturally to be expected here and there . Should a breeder, then, turn at once to wild species in an attempt to solve a problem? The answer, on the whole, must be, no . He should obviously look first at working collections or material of old and current cultivars and breeding stocks for the genetic character needed . Failing this, a search should be made through genetic

Environmental Interaction and The Genetics of Flowering

Abstract: A discussion of genetic considerations that apply to plants in general is followed by reviews dealing specifically with sorghum, wheat, several grasses, Pisum, Phaseolus and other legumes

Increased induction and chromosome doubling of androgenetic haploid rye.

Abstract: Further progress of studies aimed at increasing production of androgenetic Secale cereale plants via the culture of anthers is described. Two culture media initially developed for rice and wheat anther culture have been shown to have pronounced influence on rye. It has been possible to increase the average percentages of responsive anthers (i.e. those producing embryoids or calluses) from 0.26% to 10% with a maximum in certain experiments of over 40 %. Of nearly 400 plants produced in 1976, 1/4 are green and can be grown further by transfer to potting compost; 3/4 are albino. Stable green haploid lines were present amongst the plants, and after vegetative propagation of the lines representative samples have been treated with colchicine resulting in diploid, triploid and tetraploid plants. The influence of the genetic background of the donor plants on the success rate of anther culture and on the percentage of albino formation is discussed.

Breeding for resistance in rice

Abstract: Rice is the host for more disease and insect organisms than any other cereal crop. More than 60 diseases and over 100 insect species are known to attack the rice crop. Some of these are of major international importance. During the last 10 years major changes have occurred in the varietal composition and cultural practices for rice. High yielding varieties are now planted on approximately 25% of the 130 million hectares planted to rice all over the world. These varieties are characterized by early maturity, photoperiod insensitivity, short stature, high tillering, and dark green erect leaves. Approximately 80 improved plant type varieties have replaced literally hundreds of tall traditional cultivars, thereby reducing the genetic variability of the crop. In the wake of introduction of varieties with improved plant type, farmers have started to use improved cultural practices such as more fertilizer and higher plant populations per unit area. Development of irrigation facilities and availability of early maturing, photoperiod-insensitive varieties have enabled the farmers in tropical Asia to grow successive crops of rice throughout the year on large areas. Reduced genetic variability, improved cultural practices, and continuous cropping with rice, intended for increased rice production, have increased the genetic vulnerability of the crop. Within the last few years serious outbreaks of diseases and insects on rice have occurred in several countries. Very little research has been done on the chemical control of rice diseases in the tropics. Several insecticides have been identified, but chemical control of high insect populations for prolonged periods in tropical climates where insect generations overlap throughout the year is very expensive. Social and economic conditions in the tropics present other obstacles to the chemical control of rice diseases and insects. The use of host resistance to control diseases and insects is the most logical approach to overcome these production constraints.

Level of activity of nitrate reductase at the seedling stage as a predictor of grain nitrogen yield in wheat (Triticum aestivum L.)

Abstract: The yield of grain nitrogen of 24 wheat cultivars grown in the field was found to be related to the activity of the enzyme nitrate reductase (EC1.6.6.1) in the first vegetative leaf of 21-day-old plants grown in a controlled environment. It was concluded that a cultivar's potential for yielding grain nitrogen could be predicted from the activity of nitrate reductase at the seedling stage. This could enable the plant breeder to identify, early in the selection program, lines worth keeping for more advanced testing. Harvest index for nitrogen varied considerably between cultivars, but was usually largest in cultivars with large yields of grain nitrogen. Improvement in harvest index for nitrogen should go some way towards breaking the inverse relation between grain yield and grain nitrogen percentage in plants grown on a limited supply of soil nitrogen.

Artificial mutagenesis as an aid in overcoming genetic vulnerability of crop plants.

Abstract: Artificially induced genetic variation is being used effectively to supplement or complement sources of natural origin for practical plant breeding Thus, creating genetic variation will become increasingly important as crop genetic resources become more difficult to obtain via plant exploration The artificial induction of useful genetic variation offers important elements that can be used for overcoming genetic vulnerability: (1) new, previously unknown alleles can be induced in crop plant species to broaden the base of variation; (2) useful genetic variation can be induced in modern cultivars helping to shorten breeding time or to extend production “life”; (3) characteristics of existing genetic resource stocks can be improved to make them more useful in breeding; and (4) recombination in crosses may be enhanced The performance of induced mutant crop cultivars and the successful uses of induced genetic variation in cross breeding indicate that artificial mutagenesis will play an increasingly greater role in plant breeding

Defense of the rice crop against insect pests

Abstract: About 100 different species of insects have been recorded as damaging the rice crop, and 15 of these species are pests of major economic significance. The warm and humid environment of rice fields favors the multiplication of insects, and some of these species often infest the rice crop in large numbers. Since it is probable that many of these have infested rice for centuries, it is only to be expected that rice plants have evolved some defense mechanisms, at least against some of these pests. That such defenses do occur has been verified against all of the about eight different species of insect pests that have been investigated for this purpose. Historical associations for the development of such differences, however, do not appear to be essential, as about 300 collections of Oryza glaberrimn rice from Africa were found highly resistant to the green leafhopper, Nephotettix virescens, which is not known to occur in Africa, and many varieties of Oryza sativa rice from Asia were found highly resistant to the delphacid, Sogatodes oryzicola, in South America,\" which has not been recorded from Asia. The information available on the defense of the rice plant against insect pests is limited only to pests of major economic significance as efforts have been made to develop varieties resistant to these insects. Most of this work has been done only during the last 10-15 years. Although differences in susceptibility of rice varieties to certain insect pests have been known for a long time, the knowledge was based mostly on general field observations. These recent studies have identified varieties that possess defense against insect pests; the nature of this defense has been investigated, and it has been bred into high yielding and good quality varieties. Such varieties are becoming very popular as they minimize the build up of insect infestations that otherwise appear to be favored by intensive cultivation of modern, heavy tillering, short statured varieties and greater use of nitrogenous fertilizers. The outstanding advantages of using resistant varieties as a method of insect control are that it does not involve any additional cost to the farmers, is generally compatible with other methods of pest control, and does not cause environmental pollution problems. This paper reviews the information on varietal resistance to rice pests with particular reference to the work done at the International Rice Research Institute (IRRI) .

Hybrid vigour in controlled interspecific crosses of Eucalyptus tereticornis X E. camaldulensis.

Abstract: Ten to twelve year old flowering trees of the two species growing on the New Forest estate of this Institute were used in the crossing work. The techniques employed for the emasculation, isolation and pollination of the flowers were the Same as those described earlier (VENKATESH and KEDHARNATH, 1965). The crotsses were made during the moinths of September and October, after the monsoon rains when E. tereticornis (Et) and the northern (but not the southern) form olf E. camaldulensis (Ec) flower together at New Forelst (VENKATESH and SHARMA, 1975). Details of the crosses made and the single-site field trials planted of each of the three full-sib hybrid families are given in Table 1. trials. In the case of trial No. 3 of the cross FRI-4 however, unlike the two olthers, diameter mea,surements were also made first at 30.5 Cm. height, then a t half height and finally a t breast height. Volume was computed using SMALIAN'S formula for sectional stem lengths up to half height.

Recurring off-types in lettuce: Their significance in plant breeding and seed production

Abstract: The lettuce cv. Valentine regularly produces non-heading off-type plants at the relatively high frequency of 4 × 10−3. They result from mutation to the dominant condition. A similar propensity has been reported twice before in lettuce; it is highly heritable.

On the Advances of Plant Breeding

Abstract: Plant breeding started with sedentary agriculture and particularly the domestication of the first agricultural plants, a practice which is estimated to date back 9,000 to 11,000 years. Initially early farmers simply selected food plants with particular desirable characteristics, and employed these as progenitors for subsequent generations, resulting in an accumulation of valuable traits over time.