Seed priming is a pre-sowing treatment which leads to a physiological state that enables seed to germinate more efficiently. The majority of seed treatments are based on seed imbibition allowing the seeds to go through the first reversible stage of germination but do not allow radical protrusion through the seed coat. Seeds keeping their desiccation tolerance are then dehydrated and can be stored until final sowing. During subse‐ quent germination, primed seeds exhibit a faster and more synchronized germination and young seedlings are often more vigorous and resistant to abiotic stresses than seedlings obtained from unprimed seeds. Priming often involves soaking seed in predetermined amounts of water or limitation of the imbibition time. The imbibition rate could be somehow controlled by osmotic agents such as PEG and referred as osmopriming. Halopriming implies the use of specific salts while "hormopriming" relies on the use of plant growth regulators. Some physical treatments (UV, cold or heat,..) also provide germination improvement thus suggesting that priming effects are not necessarily related to seed imbibition. A better understanding of the metabolic events taking place during the priming treatment and the subsequent germination should help to use this simple and cheap technology in a more efficient way.

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Seed Priming: New Comprehensive Approaches for an Old Empirical Technique

Transcriptional regulation of bHLH during plant response to stress

Breeding for disease resistant varieties remains very effective and economical in controlling the bacterial leaf blight (BLB) of rice. Breeders have played a major role in developing resistant rice varieties against the BLB infection which has been adjudged to be a major disease causing significant yield reduction in rice. It would be difficult to select rice crops with multiple genes of resistance using the conventional approach alone. This is due to masking effect of genes including epistasis. In addition, conventional breeding takes a lot of time before a gene of interest can be introgressed. Linkage drag is also a major challenge in conventional approach. Molecular breeding involving markers has facilitated the characterization and introgression of BLB disease resistance genes. Biotechnology has brought another innovation in form of genetic engineering (transgenesis) of rice. Although, molecular breeding cannot be taken as a substitute for conventional breeding, molecular approach for combating BLB disease in rice is worthwhile given the demand for increased production of rice in a fast growing population of our society. This present article highlights the recent progress from conventional to molecular approach in breeding for BLB disease resistant rice varieties.

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Bacterial leaf blight resistance in rice: a review of conventional breeding to molecular approach.

Bacterial leaf blight (BLB) is one of the most serious threats to the rice crop in irrigated and rainfed areas of the world. It is caused by Xanthomonas oryzae pv. oryzae and has been known for more than a century. Through rigorous screening and selection, a number of resistant cultivars have been produced and utilized, but resistance was overcome by the development of mutant strains of pathogen and by the dynamic change in Xoo populations. About 38 resistance genes have been reported in rice against the disease and a few have been cloned. The pyramiding of several resistance genes through marker assisted selection has been a quite effective strategy for combating the disease. However, new powerful tools such as transgenics have been introduced to make a significant impact. The purpose of this mini-review is to consolidate the existing knowledge about bacterial leaf blight in rice and the progress made both in conventional as well as in molecular dimensions of breeding together with potential findings and constraints.

Breeding approaches for bacterial leaf blight resistance in rice (Oryza sativa L.), current status and future directions

The present experiment was carried out to study the influences of exogenously-applied nitric oxide (NO) donor sodium nitroprusside (SNP) and hydrogen peroxide (H2O2) as seed primers on growth and yield in relation with different physio-biochemical parameters, antioxidant activities, and osmolyte accumulation in wheat plants grown under control (100% field capacity) and water stress (60% field capacity) conditions. During soaking, the seeds were covered and kept in completely dark. Drought stress markedly reduced the plant growth, grain yield, leaf photosynthetic pigments, total phenolic content (TPC), total soluble proteins (TSP), leaf water potential (Ψw), leaf turgor potential (Ψp), osmotic potential (Ψs), and leaf relative water content (LRWC), while it increased the activities of enzymatic antioxidants and the accumulation of leaf ascorbic acid (AsA), proline (Pro), glycine betaine (GB), malondialdehyde (MDA), and H2O2. However, seed priming with SNP and H2O2 alone and in combination mitigated the deleterious effects of water stress on growth and yield by improving the Ψw, Ψs, Ψp, photosynthetic pigments, osmolytes accumulation (GB and Pro), TSP, and the antioxidative defense mechanism. Furthermore, the application of NO and H2O2 as seed primers also reduced the accumulation of H2O2 and MDA contents. The effectiveness was treatment-specific and the combined application was also found to be effective. The results revealed that exogenous application of NO and H2O2 was effective in increasing the tolerance of wheat plants under drought stress in terms of growth and grain yield by regulating plant-water relations, the antioxidative defense mechanism, and accumulation of osmolytes, and by reducing the membrane lipid peroxidation.

https://www.mdpi.com/2223-7747/9/2/285/pdf

Use of Nitric Oxide and Hydrogen Peroxide for Better Yield of Wheat (Triticum aestivum L.) under Water Deficit Conditions: Growth, Osmoregulation, and Antioxidative Defense Mechanism.

Aromatic basmati rice is vulnerable to bacterial blight disease. Genes conferring resistance to bacterial blight have been identified in coarse rice; however, their incorporation into basmati varieties compromises the prized basmati aroma. We identified bacterial blight resistance genes Xa4, xa5, Xa7, and xa13 in 52 basmati landraces and five basmati cultivars using PCR markers. The Xa7 gene was found to be the most prevalent among the cultivars and landraces. The cultivars Basmati-385 and Basmati-2000 also contained the Xa4 gene; however, xa5 and xa13 were confined to landraces only. Ten landraces were found to have multiple resistance genes. Landraces Basmati-106, Basmati-189 and Basmati-208 contained Xa4 and Xa7 genes. Whereas, landraces Basmati-122, Basmati-427, Basmati-433 were observed to have xa5 and Xa7 genes. Landraces Basmati-48, Basmati-51A, Basmati-334, and Basmati-370A possessed Xa7 and xa13 genes. The use of landraces containing recessive genes xa5 and xa13 as donor parents in hybridization with cultivars Basmati-385 and Basmati-2000, which contain the genes Xa4 and Xa7, will expedite efforts to develop bacterial blight-resistant basmati rice cultivars through marker assisted selection, based on a pyramiding approach, without compromising aroma and grain quality.

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Detection of bacterial blight resistance genes in basmati rice landraces.

Being macronutrient, K+ is involved in a number of metabolic processes including stimulation of over 60 enzymes. The present study was conducted to investigate whether K-priming could alleviate the effects of salinity on the growth and nutrient status of cotton seedlings. The seeds of two cotton cultivars, namely FH-113 and FH-87, were primed with solutions of three potassium sources (KNO3, K2SO4 and K2HPO4) using three concentrations (0%, 1.25% and 1.5%) of each potassium source. After 1 week of germination, the seedlings were subjected to salinity (0 and 200 mM NaCl) stress. The results showed that salinity significantly affected growth and nutrients status of cotton seedlings. The K-priming alleviated the stress condition and significantly improved dry matter as well as nutrient uptake in cotton seedlings. Of the priming treatments pre-sowing treatment with KNO3 (1.5%) was most effective in increasing shoot and root lengths and biomass of cotton seedlings. The seedlings raised from seed treated...

K-priming positively modulates growth and nutrient status of salt-stressed cotton (Gossypium hirsutum) seedlings

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Nitric oxide regulated improvement in growth and yield of rice plants grown under salinity stress: antioxidant defense system.

Morpho-physiological responses of cotton (Gossypium hirsutum) to salt stress.

Salinity is a multidimensional stress affecting crop yield and productivity at various levels of plant organization. To assess salt induced adverse effects on cotton (Gossypium hirsutum L.), ten cultivars were grown in sand culture supplemented with full strength Hoagland's nutrients solutions and different salt concentrations (0, 50, 100 and 200 mM NaCl). Salt stress markedly reduced growth attributes, relative water contents, efficiency of photosystem II, net CO2 assimilation rate (A), transpiration rate (E) and stomatal conductance in all cultivars. Reduction was maximum at the highest level of salt stress i.e. 200 mM. However, response of cotton cultivars was variable to various levels of salinity and even at various developmental stages. Cultivars RH-510, BH-118 and MNH-770 were ranked as relatively salt tolerant on the basis of their better growth performance and net CO2 assimilation rate whereas cvs. CIM-496, CIM-473 and FH-901 were relatively salt sensitive. Cultivars RH-510, BH- 118 and MNH-770 exhibited high shoot fresh and dry weights, photosynthetic rate (A), and Photosystem II (Fv/Fm) efficiency at both seedling and maturity growth stages. Results suggest that selection of plants having high photosynthetic rate and biomass at seedling stage may be a good source of high yield at mature stage of growth.

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Huma Lubna Shaheen

Papers

Detection of bacterial blight resistance genes in basmati rice landraces.

K-priming positively modulates growth and nutrient status of salt-stressed cotton (Gossypium hirsutum) seedlings

Nitric oxide regulated improvement in growth and yield of rice plants grown under salinity stress: antioxidant defense system.

Morpho-physiological responses of cotton (Gossypium hirsutum) to salt stress.

Salt-induced effects on some key morpho-physiological attributes of cotton (Gossypium hirsutum L.) at various growth stages.