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An improved procedure has been developed for high frequency androgenesis in an elite long duration indica rice hybrid. The effects of cold temperature pretreatment, duration of treatment and media with different plant growth regulators on callus induction and shoot regeneration were examined for generation of doubled haploids. N6 medium supplemented with 2.0 mg l −1 2,4-D, 0.5 mg l −1 BAP and 30 g l −1 maltose was found to be most effective for callusing when compared with MS and SK1. The N6 media grown calli showed maximum green shoot regeneration frequency in MS medium supplemented with 0.5 mg l −1 NAA, 0.5 mg l −1 Kinetin, 1.5 mg l −1 BAP and 30 g l −1 sucrose after 2 week of culture. The cold temperature treatment of spike at 10°C for 2 days alongside by 8 days was found to be most suitable conditions for callusing and green shoot regeneration producing 186 green plants from indica rice hybrid, CRHR32. The ploidy status assessed on the basis of morpho-agronomic characters revealed fertile diploids at a frequency of about 81.10%; 16.10%, 2.68% and 1.08% were polyploids, haploids and mixploids respectively. Microsatellite marker analysis showed 1 : 1 ratio of the alleles of CMS and restorer lines used for development of CRHR32. Homozygosity was detected for all the marker loci in 150 DHs and only one plant was identified as heterozygote. This investigation identified the favorable media composition and condition for callus induction and green plant regeneration which would further increase the knowledge and better understanding in rice hybrids for development of DHs.

RNAi mediated gene silencing demonstrated to serve as a defence mechanism against abiotic stress. Some endogenous small RNAs (microRNA and siRNA) have emerged as important players in plant abiotic stress response. Drought and salinity are the major environmental stresses that limit the agricultural food production. miRNA involved in drought and salinity stress response, including ABA response, auxin signalling, osmoprotection and antioxidant defence by downregulating the response target gene. It is observed that some of the microRNAs are upregulated or downregulated in response to drought and salt stress. We reviewed that miR167, miR393, mir474, miR169g are upregulated whereas miR168, miR396, miR397 are downregulated in rice plant during drought stress. Moreover, our detail categorical analysis on the basis of mechanism of action found that miRNA involved in drought stress was 28% in ABA signalling and response, 14.2% in auxin signalling, 9.52% in miRNA processing, 14.2% in cell growth, 9.52% in antioxidant defence, 4.76% in CO2 fixation and 9.52% in osmotic adjustment. Similarly, miRNA involved in salinity stress was 5.8% in auxin signalling, 23.5% in vegetative phase change and root, shoot, leaf and vascular development, 11.76% in gynoecium and stamens development, 8.82% in metabolic adaptation, 2.74% in early embryogenesis and 41.17% not known. Importantly, some common miRNAs such as miR159, miR167, miR169, miR393 and miR397 play an important role in both drought and salinity stress conditions. Here, in this review, we mainly focused on the current status of miRNAs, mechanism of action and their regulatory network during drought and salinity stress in plants.

Twenty-three lines from a mutagenized Bangladeshi BARI Gom-25 wheat population that included previously identified salt-tolerant lines, and the BARI Gom-25 control variety, were cultivated in a drip-irrigated salinity test field at Salt Farm Texel, Netherlands, to assess their performance during salt stress in European climatic conditions. Lines were tested at irrigation salinity levels of 1, 4, 8, 12, 16, and 20 dS m−1 in four repetitions of plots with 24 plants per plot. Average plant height, tiller number, spike length, frequency of live plants, and total grain weight (TGW) were recorded as functions of seasonal mean pore water salinity in the soil. Increases in salinity triggered reductions in all evaluated variables of the assessed lines and the control variety. However, nine mutagenized lines had at least twofold higher mean TGW than the control variety, 18.73 ± 4.19 g/plot at 1–16 dS m−1 salinity levels. Common models of salt tolerance confirmed this pattern, but there were no clear differences in salinity tolerance parameter estimates between the mutagenized lines and the control variety. Thus, despite the apparent similarity in responses of all lines to salinity increase, we clearly identified lines that tended to have higher TGW at given salinities than the control variety. This higher TGW at the full range of salinity treatments indicates not only a possible higher salinity tolerance but a higher yield potential as well. The mechanisms involved clearly warrant further attention.

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