Molecular markers: It’s application in crop improvement

Over the past few decades, plant genomics research has been studied extensively bringing about a revolution in the field of plant biotechnology. Molecular markers, useful for plant genome analysis, have now become an important tool in crop improvement. The development and use of molecular markers for the detection and exploitation of DNA polymorphism is one of the most significant developments in the field of molecular genetics. The presence of various types of molecular markers, and differences in their principles, methodologies and applications require careful consideration in choosing one or more of such methods. No molecular markers are available yet that fulfill all requirements needed by researchers. In this article we attempt to review most of the available DNA markers that can be routinely employed in various aspects of plant genome analysis such as characterization of genetic variability, genome fingerprinting, genome mapping, gene localization, analysis of genome evolution, population genetics, taxonomy, plant breeding, and diagnostics. The emerging patterns make up a unique feature of the analyzed individual and are currently considered to be the ultimate tool for biological individualization.     

Associations and genetics of three components of slow rusting in leaf rust of wheat

Summary Forty F₆ lines, the two parental lines, and a susceptible check cultivar of wheat (Triticum aestivum L.) were inoculated in the young flag leaf stage with leaf rust (Puccinia recondita f.sp. tritici) and evaluated for latent period, receptivity, and uredinium size in a greenhouse experiment. Genotypic (r_g) and phenotypic (r_p) correlations between latent period and uredinium size were –0.81 and –0.62, respectively. A negative correlation (r_g=–0.50, r_p=–0.41) was found between latent period and receptivity and a positive correlation (r_g=0.28, r_p=0.26) between uredinium size and receptivity was found. Area under the disease progress curve (AUDPC) and final rust severity (FRS) obtained from a subsequent field study with common entries were negatively correlated with latent period and positively correlated with uredinium size. Correlations of receptivity with both AUDPC and FRS were not significant. The distributions of F₆ family mean uredinia size and latent period were continuous between slow rusting and fast rusting parents: however, the distribution for receptivity was discrete. Narrow-sense heritability estimates were 63%, 57%, and 47% for uredinium size, latent period, and receptivity, respectively. Estimates of the minimum number of effective factors were three for latent period and three or four for the uredinium size and receptivity. The components are controlled by closely linked genes or due to pleotropic effects of the same gene.Abbeviations AUDPC - Area under the disease progress curve - FRS - Final rust severity     

Plant diversity at Chilapatta reserve forest of Terai Duars in sub-humid tropical foothills of Indian eastern Himalayas

From March 2007 to March 2009 we quantified plant diversity at Chilapatta Reserve Forest in Terai Duars in the Indian eastern Himala-yas. We sampled stratified random nested quadrats. Species richness was 311, representing 167 genera and 81 families. The species diversity index and concentration of dominance of the forest were 2.20 and 0.0072, respectively. Shannon-Wiener index and evenness indices were 4.77 and 1.44, respectively. The Importance Value Index （IVI） of species ranged from 0.13 to 37.94. The estimated diversity indices indicated heterogene-ity of the forest in its composition, structure, function and dynamics. Rich forest plant diversity supports the need for continued conservation of tropical forests.     

Litter production and decomposition in the forested areas of traditional homegardens: a case study from Barak Valley,Assam, northeast India

Homegardens are one of the oldest forms of managed land use systems characterised by high diversity and complexity of their species structure which in turn contribute to efficient nutrient cycling. Litterfall and decomposition are the two major processes that replenish the soil nutrient pools and endow sustainability to these agroforests. A study was carried out in the village Dargakona, Barak Valley, northeast India to understand the pattern of litter production and litter decomposition in the traditional homegardens. Annual litter production was 6.27 Mg ha⁻¹ with a bimodal distribution pattern and the nitrogen input through litterfall accounted for 48.17 kg ha⁻¹ year⁻¹. Litter decomposition studies for ten multipurpose trees revealed Sapium baccatum and Toona ciliata to be the most labile litter species and the decay rate coefficients varied among the species with differing rates of nutrient release pattern. Such studies can provide information regarding the litter quality of indigenous tree species and help validate farmers planting and management of multiple species which allows for efficient nutrient cycling of the system.     

印度阿鲁纳恰尔邦温带阔叶混交林树桩周长和高度对受干扰的树形杜鹃再发芽的影响

Sprout contribution to natural regeneration of Rhododendron arboreum following the tree felling for fuel wood and other purposes was studied in two disturbed sites (Paipraw and Falockchar) of Rhododendron forest in Arunachal Pradesh, northeast India. Cut stumps were categorized into seven girth and height classes to evaluate the effect of stump girth and height on production of sprouts. Effect of stump girth on survival of sprouts was also investigated. Results show that highest number of cut stumps is recorded in medium girth classes (50–80, 80–110, and 110–140 cm) in both Paipraw and Falockchar stands. However, density of cut stumps is higher in Paipraw (1 210 stumps·ha⁻¹) than Falockchar (1 154 stumps·ha⁻¹). Nevertheless, a little higher percentage of sprouting is recorded in Falockchar (18%) than that of Paipraw (15%). Similarly, maximum number of cut stumps is observed in the medium height classes (50–80, 80–110 and 110–140 cm) in both the sites. Cut stumps with lower girths show greater ability of sprouting than that of larger girth classes. Significant correlations are observed between stump girth and sprout number and between stump height and number of sprouts. Survival of sprouts also depends on stump girth. Survival of sprout shows significant variations between different sampling times in both the sites. Though overall sprout regeneration of R. arboreum is very poor, sprouts arising from lower girth classes survive well than those of higher girth classes. The findings of this investigation signify that stump sprouting is not playing much role in the natural regeneration of R. arboreum though it has the ability to sprout. Sprout survival is not adequate to restore a stand where indiscriminate tree felling is continued and the species may be considered as a poor coppicer. Therefore, regeneration through seeds and seedlings should be preferred over regeneration through sprouting.     

Diversity and structural composition of species in dipterocarp forests: a study from Fasiakhali Wildlife Sanctuary,Bangladesh

Fasiakhali Wildlife Sanctuary is a protected area composed of tropical remnant rainforest that harbor substantial number of large,old Garjan(Dipterocarpus spp.)trees.The present study assessed composition,structure and diversity of the species in this protected area.A total of 32 trees species were recorded with DBH ≥ 11 cm belonging to 24 genera and 19 families.The forest is low in plant diversity as represented by Shannon–Wiener diversity and Simpson Dominance indices.Dipterocarpus turbinatus was the most dominant species with maximum relative density,frequency,dominance,and importance value index.Syzygium firmum and Tectona grandis followed in terms of dominance.The structural composition indicated higher number of individuals in the medium growth classes(41 to 511 cm DBH and 16–20 m height ranges),whereas D.turbinatus was the only species that dominated most of the growth classes.Poor stem density in lower growth classes indicated meager recruitment of regeneration which may be due to lower annual precipitation,increased grazing and encroachments.This study will help to understand the patterns of tree species composition and diversity in the remnant dipterocarp forests of Bangladesh.It will also contribute to identifying threatened plants to undertake D.turbinatus based conservation and sustainable management of the Fasiakhali Wildlife Sanctuary.     

Aphidicidal activity of some indigenous plant extracts against bean aphid <Emphasis Type="Italic">Aphis </Emphasis><Emphasis Type="Italic">craccivora</Emphasis> Koch (Homoptera: Aphididae)

Aphidicidal activity of hot and cold water extracts of some indigenous plants, Azadirachta indica A. Juss (neem), Calotropis procera (Aiton) W.T. Aiton (akanda), Polygonum hydropiper L. (biskatali) and Ipomoea sepiaria J. Koenig ex Roxb. (bankalmi), were tested against the bean aphid, Aphis craccivora Koch. Hot water extract of P. hydropiper and A. indica was found to be the most effective (87.6–94.5 and 80.47–89.6% mortality respectively, P < 0.01) among all the extracts. Other hot and cold water extracts also appeared to be useful (59.5–87.5% mortality) as pesticides for A. craccivora. The highest yield (3.25 kg per plant) was obtained using hot water extract of P. hydropiper followed by hot water extract of A. indica (3.15 kg per plant). The lowest yield (0.32 kg per plant) was recorded from the control block. All the phytoproduct treatments had significantly (P < 0.01) better yield than the control block.     

Variation in sensitivity to streptomycin-induced bleaching and dark-induced senescence of rice (<Emphasis Type="Italic">O. sativa</Emphasis>) and ragi (<Emphasis Type="Italic">E. coracana</Emphasis>) genotypes and their relationship with yield and adaptability

Variation in streptomycin sensitivity and dark sensitivity of 36 rice genotypes of three different maturity groups and 30 ragi genotypes of two different maturity groups were studied. Streptomycin sensitivity and dark sensitivity of rice and ragi genotypes were expressed in terms of bleaching index (BI) and senescence index (SI), respectively. Genotypes of each maturity group of each crop showed wide variation in their BI / SI values. The objective of this investigation was to find the relationship of the BI / SI parameter with yield, adaptability, and stability in yield performance of rice and ragi genotypes. Yield performance of rice and ragi genotypes were evaluated over 12 and nine environments, respectively. Adaptability and stability analysis were done following the linear regression model of Eberhart and Russell (1966) and the AMMI Stability Value (ASV) of Purchase (1997). BI parameter showed a positive correlation with yielding ability and deviation from regression (S2d) in both rice and ragi, and a negative correlation with adaptability parameter (b) for all the maturity groups of rice and ragi except in the early ragi group. SI parameter showed a negative correlation with yielding ability for all the maturity groups of rice and ragi except in the early ragi group and a positive correlation with adaptability parameter (b) for all the maturity groups of rice and ragi. This experimental study revealed that sensitivity of rice genotypes to streptomycin (SM) in terms of BI could be used to predict yielding ability of genotypes, and dark sensitivity (SI) could be used to indicate adaptability to rich and poor environments. This novel approach may help the breeder in indirect selection of high-yielding genotypes and genotypes well-adapted to rich or poor environments at an early seedling stage before going for multilocation trials.