Gene-for-gene relationship for resistance in wheat to isolates of Karnal bunt, Neovossia indica

Reactions to eight isolates of Karnal bunt, Neovossia indica, collected from seven different locations in northern India were studied on 13 host lines, including cultivars and breeding lines of Triticum aestivum, Triticum durum and Triticosecale in all possible combinations. The incidence of Karnal bunt varied from zero in PBW 34 and PBW 248 with isolates Ni8 and Ni2, respectively, to as high as 66.8% in a highly susceptible cultivar WL 711 with isolate Ni5. The differences in disease incidence among cultivars and isolates were highly significant. All the isolates could be distinguished on the basis of differential reactions on one or more of the host lines. Even the most resistant lines of durum (PDW 215), triticale (TL 1210) and wheat (HD 29) could be distinguished by the differential disease reaction with one or more of the eight isolates. The cultivar-isolate interaction for disease score was highly significant, indicating the probable existence of a gene-for-gene relationship in this host-pathogen system.     

Chromosomal Stability in the Backcross Progenies of Pentaploid Hybrids between Avena sativa L. and A. maroccana Gdgr.

In a backcrossing programme to transfer desirable characters from wild Avena maroccana Gdgr. to cultivated oats, A. sativa L., meiotically stable plants in BC₁F₃ and BC₂F₂ progenies were isolated. The recovery of stable genotypes with 2n = 6×= 42 chromosomes indicated that two backcrosses are enough for such a programme. The cytological observations in various backcross generations are presented and discussed.     

The Cytological Status of Plants Regenerated from Shoot-Meristem Culture of Pisum sativum L

The cytological status of plantlets regenerated from shoot apical meristems of Pisum sativum was investigated. Chromosome counts in root apices of in vitro regenerated plants showed a preponderance of diploid cells. Moreover, the karyotypes of root-tips from plants derived from culture and from normal plants were basically the same. Topics such as the treatment of chromosomal armlength data, simple statistical comparison of samples derived from normal and regenerated plants are discussed.     

Plant Regeneration from in vitro Cultured Anthers of Black Mustard (Brassica nigra Koch)

Anthers of Brassica nigra, excised from fresh as well as cold-pretreated (3 days at 3 ± 2°C) buds cultivated on modified B₅ medium (Gamborg et al. 1968) containing sucrose level varying from 2 % to 10 %, along with 1O^?6M BAP (benzylaminopurine) and 9 × 10^?6M 2,4-D (2,4-dichlorophenoxyacetic acid), developed calli and/or embryos. The latter response was observed only in anthers reared on media containing 6 % or higher levels of sucrose. On media containing two or four per cent sucrose, the anthers produced calli, exclusively. The growth of embryos was inhibited or else they started callusing if left on the media containing higher levels of sucrose. However, on transfer to MS medium (Murashige and Skoog 1962), containing 2 % sucrose, embryos started callusing and subsequently a few secondary embryos differentiated. Such embryos were sub-cultured on MS + 5 × 10^?6M BAP + 2 % sucrose, wherein numerous shoots developed from embryos. The shoots were rooted by transferring to a medium containing 5 × 10^?6M NAA (naphthalene acetic acid). Within two months of culture, some of these plants started flowering in vitro.     

Metroglyph analysis of Indian and exotic varieties of maize

Summary Metroglyph and index score analysis was carried out with 15 Indian and 15 exotic varieties of maize currently being used in the breeding programme of the Coordinated Maize Improvement Project at the Indian Agricultural Research Institute. It was found that the Indian varieties under study fall into three morphological complexes which differed among themselves. The variability pattern of the second and third Indian complexes resembled that of Mexican and Colombian germ plasm. The variability pattern of the Caribbean germ plasm was different from the Indian complexes. Index score analysis also gave similar results. Previous breeding experiments also confirmed the findings that these varieties might have originated from a few Mexican or Colombian introductions.     

Widening the gene pool of cultivated lentils through introgression of alien chromatin from wild Lens subspecies

Wild Lens species/subspecies are a potential source for increasing genetic diversity in cultivated lentil. Four intraspecific crosses were attempted between cultivated and wild lentils. Viable hybrids were produced between L. culinaris ssp. culinaris × L. culinaris ssp. orientalis and L. culinaris ssp. culinaris × L. culinaris ssp. odomensis. Normal meiosis and pollen fertility were observed in the first set of crosses, whereas chromosomal abnormalities and reduced pollen fertility were observed in the second set of crosses. These crosses were also studied for some quantitative traits. The range, mean and coefficient of variation were calculated in parents, F₁, F₂ and BC₁ generations to determine the extent of variability generated in the cultivated lentil through introgression of genes from wild lentil. The cultivated lentil × L. culinaris ssp. orientalis crosses showed substantially higher variability for all the traits than crosses involving cultivated lentil ×L. culinaris ssp. odomensis. The results of the present study indicated that these wild subspecies can be exploited for breeding purposes and their variation can easily be utilized to widen the genetic base of the cultivated lentil.     

Male-sterility in the grain amaranth (Amaranthus hypochondriacus ex-Nepal) variety Jumla

Summary Twenty naturally occurring male-sterile plants were recovered from a normal population of the grain amaranth, variety Jumla. The identification of the male-sterile plants is possible during anthesis and after flowering. The male-sterility in this variety is conditioned by a single recessive nuclear gene ms.This research was supported by Grant No. AMA-KE-4-83-22 (CRG GRANT) from the National Academy of Science, USA. Reprint requests to V.K. Gupta.     

Genetic Analysis of Resistance to Xanthomonas campestris pv. oryzae (Ishiyama) Dye in a Rice Breeding Line ARC 10464

The genetics of resistance to three Indian pathotypes of Xanthomonas campestris pv. oryzae, namely, IX01, IX08 and IX09, was studied in a landrace of Indica rice ‘ARC 10464’. Resistance to each of the two pathotypes IX01 and IX09 was governed by two independently-inherited dominant genes while a single dominant gene was operative against patho-type 1X08. The joint segregation tests conducted on F₂ plant progenies (F₃ families) using pathotypes IX01, IX08 and IX09 suggested that the gene/(s) effective against each of the pathotypes are different.     

Effect of Water Stress on Physiological Attributes and their Relationship with Growth and Yield of Wheat Cultivars at Different Stages

The effects of water stress on physiological attributes of drought‐sensitive (Kalyansona) and drought‐tolerant (C‐306) wheat cultivars were studied in a pot experiment. Water stress was imposed by withholding irrigation at boot and anthesis stages. Leaf water potential, leaf osmotic potential and leaf turgor potential (measured with pressure chamber and osmometer), as well as leaf diffusive resistance, leaf transpiration rate and leaf‐to‐air transpiration gradient (measured with a steady‐state porometer) were measured diurnally. Growth and yield parameters were recorded after harvesting of the crop. Triplicate data were analysed using a completely randomized design and correlations amongst these parameters were computed. Water stress was found to reduce diurnal leaf water potential and leaf osmotic potential in both the genotypes but leaf osmotic potential was significantly higher in the drought‐tolerant cultivar C‐306 than in the drought‐sensitive cultivar Kalyansona. Positive turgor was recorded in both the genotypes under water stress and non‐stress conditions. Water‐stressed plants showed significantly lower turgor potential than control plants. In diurnal observations, water‐stressed plants exhibited significantly higher leaf diffusive resistance in both genotypes at both stages. The diffusive resistance of C‐306 was predominantly higher than that of Kalyansona. Water stress decreased leaf transpiration rate at both stages but the reduction was higher at the anthesis stage. The leaf‐to‐air temperature gradient was much higher in C‐306 than in Kalyansona at the boot stage but at the anthesis stage genotypic variation was non‐significant. The capacity to maintain cooler foliage was lower at the anthesis stage than at the boot stage in both the cultivars. Shoot dry weight, number of grains, test weight, grain yield, biological yield and harvest index decreased to a greater extent when water stress was imposed at the anthesis stage, while imposition of water stress at the boot stage caused a greater reduction in plant height and number of tillers. Similarly, water stress caused a smaller reduction in growth, yield and yield attributes in C‐306 than in Kalyansona. In general, the correlation coefficient of grain and biological yield with water potential and its components was positive and highly significant. Similarly, turgor potential was also correlated positively and significantly with grain yield at both the stages, but with biological yield it was significant only at the anthesis stage. A negative and significant correlation was obtained for diffusive resistance and leaf‐to‐air temperature gradient with grain yield at the boot and anthesis stages. The rate of transpiration was also positively and significantly correlated to grain and biological yields at both the stages. Amongst the yield attributes, number of leaves and number of tillers were positively correlated at the anthesis stage, whereas leaf area and shoot dry weight were significantly correlated with grain and biological yields at both the stages.