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September 2008

Table of Contents

High temperature and salt stress response in French bean (Phaseolus vulgaris)                       .                                                                   
Nagesh Babu R., Devaraj Varadahally Rangaiah              Pages 40-48 (Full text PDF)

Abiotic stresses, such as high temperature, and salt stress are major factors which reduce crop productivity.  Effects of  high temperature (46-48 C) and salt stress (0.4 M) on French bean (Phaseolus vulgaris), a major vegetable crop, were  evaluated in terms of antioxidants and antioxidant enzymes in S-9 cultivar. Both stresses caused similar responses in  the plant. Oxidative stress indicators such as H2O2, TBARS, glutathione, ascorbic acid, and proline were significantly  elevated.  Similarly, antioxidant enzyme, guaiacol-specific peroxidase (POX) was significantly elevated. Other enzymes,  Beta-amylase and acid phosphatase (AP) activities were marginally enhanced. However, stresses had contrasting  effects on glutathione reductase (GR) and catalase (CAT), which were drastically reduced in temperature stress, and  elevated in salt stress. No variations were observed in AP, POX, and CAT isozymes. Patterns of GR and Beta-amylase  isozymes differed between temperature and salt stress.  SDS-PAGE indicated entirely different sets of proteins in  temperature and salt stressed seedlings. Growth rate and fresh mass were affected to same extent, relative to their  respective controls. DNA damage was more pronounced under temperature stress than under salt stress. Response  mechanism of French bean appears to involve some players which are common to both the stresses, and few specific to  individual stress.

Keywords: Antioxidants; Antioxidant enzymes; French bean; Isozymes; Temperature stress; Salt stress

Genetic architecture of genes from the wild potato plant (Solanum pinnatisectum) showing resistance to the Colorado potato beetle                                           

Sanjib Nandy, Qin Chen, Jiliang Yang, Mark Goettel     Pages 49-56 (Full text PDF)                            

The Mexican wild potato species Solanum pinnatisectum is an important gene source for resistance to Colorado potato  beetle and late blight. Diploid progenies segregating for resistance genes to Colorado potato beetle were developed by  crossing S. pinnatisectum with S. cardiophyllum. The hybrid lines were resistant to Colorado potato beetle. A resistant  hybrid line from this cross was selected and backcrossed as a female to S. cardiophyllum to generate a backcross  progeny. This backcross progeny was tested for genetic architecture of the Colorado potato beetle resistance gene.  Resistance percentage of the test lines over the control was determined for statistical analysis. The Chi square test  result showed a significant 1:3 (resistance: susceptible) ratio in this backcrossing population, indicating that resistance  in S. pinnatisectum to Colorado potato beetle may be controlled by two independently segregating major genes having  two respective loci, acting in a complementary epistatic manner. The availability of Colorado potato beetle resistance  genes, along with late blight resistance genes in S. pinnatisectum may enable breeders and geneticists to develop a  single cultivar through the gene pyramiding method.

Keywords: Colorado potato beetle, backcross, potato, resistance genes

Molecular responses of Bt transgenic corn (Zea mays L.) plans to salt (NaCl) stress          

Mohamed Salah Beltagi                                                 Pages 57-63 (Full text PDF)                                                            

Non-transformed and Bt transgenic crop lines of a hybrid (YieldGard 2) corn (Zea mays L.) plants in the 4th leaf stage  were subjected to 0, 50, 100 and 150 mM NaCl. Significant (P = 0.05) reduction in growth of non-traformed plants was  recorded under almost all levels (50, 100 and 150 mM) of salt (NaCl) stress; while, the growth of the Bt transgenic corn  plants showed no significant changes under the same levels of salt stress. Chlorophyll a contents were reduced at 150  mM NaCl only; but did not change in the BT transgenic corn plants. Chlorophyll b was not responsive to NaCl treatments  in both non-transformed and Bt transgenic corn plants. Chlorophyll stability index (CSI) were always higher in the Bt  transgenic than in the non-transformed corn plants under all salinity levels. The analyses of SDS-PAGE revealed relative  stability in the patterns of protein bands in the Bt transgenic corn plants under salinity stress. The sum of optical  densities of protein bands was higher in the Bt transgenic corn plants. In response to salinity stress, a group of  polypeptide (76.96, 59.38, 41.56, 33.5 and 31.26 KDa) were newly synthesized in both non-transformed and Bt  transgenic plants. Salt-susceptible polypeptides of molecular weights 325.47, 32.64 and 24.17 KDa were found only in  non-transformed corn plants and completely disappeared under all level of salt stress; while two polypeptides of  molecular weights 38.59 and 30.61 KDa were totally inhibited in all salt-stressed corn plants. The synthesis of another  four polypeptides (298.81, 99.82, 20.79 and 19.43 KDa) was solely specific to the Bt transgenic corn plants. Stability of  chlorophyll pigments and molecular weights of salt stress responsive proteins are key genetic determinants of salt  stress in Bt transgenic corn plants.

Keywords: Bt Transgenic corn, CSI, salt stress, SDS-PAGE, proteins.

Mulberry wild species in India and their use in crop improvement A review                           

A Tikader, Kamble C K 
                                                Pages 64-72 (Full text PDF)                                                                     

Exploitation of wild relatives of crop plants to a large extent depends on the efficient use of germplasm resources  available in natural habitat and the centre of diversity. The primary objective for breeding is to identify the mulberry  germplasm, which will be used as a parent. This includes the performance of individual accessions with regards to their  origin, passport data, characterization, and evaluation through a series of tests in field. The crop improvement is the  transfer of desired genes and gene combination from unadapted sources into most usable breeding materials. To bring  greater diversity into the breeding pool, it requires introduction of exotic and wild materials. The breeders find it difficult to  use unadapted materials from wild source. The intermediate materials produced after incorporating the new genes is  treated as genetically enhanced materials, which may be useful to develop desired lines. The use of wild mulberry  species is limited and concentrated effort requires utilizing them. The variability, secondary and tertiary characters may  be identified from the wild gene pools to develop resistant genotypes and to utilize the resources efficiently for crop  improvement.

Keywords: Wild gene pools, breeding, secondary, tertiary genes, and crop improvement

Dynamic QTL analysis for rice blast resistance under natural infection conditions              

Yibo Li, Changjun Wu, Yongzhong Xing, Huilan Chen, Yuqing He Pages
                                                                                                 73-82 (Full text PDF)                                                                                                                         

Dynamic analyses of rice blast resistance for the assessment of genetic and environmental effects were characterized  employing a recombinant inbred lines (RILs) population. The study was conducted at three different developmental  stages of rice using natural infection tests in two years. The number of main-effect quantitative trait loci (QTL), epistatic  QTL and their environmental interactions greatly differed across various measuring stages. Two major QTL (r11a and  r11b) both on chromosome 11 could be detected at all stages, whereas most QTL were identified only at one or two  stages in the population. It was suggested that the unstable activities of most QTL identified for blast resistance may  well be due to effects of major QTL, epistatic effects between different loci, the developmental status of rice, and the  environments in which they were grown. Comparison of QTL analysis conducted under the conditions of natural infection  and artificial inoculation was performed and drew a new conclusion that QTL analysis of plant resistance based on  natural infection would have more advantages than that based on artificial inoculation.

Keywords: Rice blast resistance, Dynamic analysis, Main-effect QTL, Epistatic interactions, QTL-by-environment  interactions

Plant growth, metabolism and adaptation in relation to stress conditions. XXI.                       
Reversal of harmful NaCl-effects in lettuce plants by foliar application with urea

Mahmoud Elbaz Younis, Mohammed Naguib Hasaneen, Adel Rezk Ahmed,                                 
Dalia Mohammed El-Bialy
                                                                                      Pages 83-95 (Full text PDF)

In relation to water control levels, administration of NaCl at low (3 dSm-1), medium (5 dSm-1) or high (7 dSm-1)  concentration, in the growth medium of the lettuce plants, induced significant decreases in growth components as well  as in the metabolites and enzymes determined, at vegetative and adult growth stages. On the other hand, significant  increases in all growth and photosynthetic components determined, as well as in carbohydrate contents and in the  activities of the antioxidant enzymes were obtained, above the water control levels, in response of treatment of lettuce  plants with urea fertilizer up to 4 %, above which urea at 5% and 6% induced significant decreases in all the above  mentioned components, throughout the entire periods of the experiments. Foliar application of urea up to 5 % to the  variously salinized lettuce plants induced significant increases in all growth components as well as in all metabolites  determined as compared with values of control-salinized plants. At 6% urea, significant decreases in growth parameters  and in metabolites determined for the variously salinized plants were apparent. Thus, foliar application of urea can, at  least, partially alleviate the inhibitory effects of salinity on growth and metabolism of lettuce plants; the magnitude of  response being most pronounced with 3-4% urea.

Keywords: antioxidant enzymes, carbohydrates, growth, Lactuca sativa, NaCl, photosynthetic efficiency, urea

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