Screening Of Rice Germplasm Research Articles

Screening of Rice Germplasm against blast disease for Identification of Resistant Sources

Rice Leaf Blast disease is caused by means of Magnaporthe oryzae is one of the major biotic stresses of rice in India. To find the leaf blast resistance sources in rice accessions, an open field investigation was carried in natural and artificial epiphytotic form during rabi seasons in 2018 and 2019. A total of 97 rice genotypes including resistant check (Tetep) and susceptible check (NLR34242 and BPT5204) were grown, in uniform blast nursery (UBN). Rice Leaf blast disease severity assessment was scored according to 0-9 scale. Among rice genotypes,21.6 % were resistant, 29.8 % moderately resistant, 21.6 % moderately susceptible, 29.8 % susceptible and 16.4 % were highly susceptible during rabi 2018 whereas only 18.5 % resistant 29.8 % moderately resistant,15.4 % moderately susceptible and 23 % were susceptible and 12.37 % to rice leaf blast disease during rabi 2019. As per result, these resistant accessions with required agronomical traits can be used in leaf blast resistance breeding program as donor parent for the development of leaf blast resistant varieties in rice.

Screening of Rice Germplasm with Physiological Traits for Identification of Heat Tolerant Genotypes

High temperature as a part of the climate change scenario is imposing a severe threat to rice production and productivity worldwide. Field experiment was conducted in ICAR-IIRR during rabi 2016–17 to screen 60 diverse rice genotypes comprising of 2 germplasm lines, 11 green super rice lines, 2 introgression lines, 8 landraces, 2 tropical japonicas and 35 released varieties including 2 checks for identification of high temperature tolerant genotypes. They were tested for their nature of thermotolerance using cell membrane thermostability, PSII activity (Fv/Fm) and paraquat tolerance test as screening criteria. There was a reduction in all the above measured traits in all the genotypes however, among the genotypes the extent of reduction varied. Among the genotypes screened, Rasi, Akshayadhan, HKR47, IR64, Assanchidiya had recorded a higher grain yield under high temperature conditions and hence could be categorized as heat tolerant whereas ADT43, Vandana, NDR359 MTU1001 and IR36 had lower yields and hence were categorized as heat susceptible. The screening traits were correlated with grain yield recorded under high temperature. Positive and significant association was noted between cell membrane thermostability, Fv/Fm measured under high temperature stress with the grain yield. The tolerant genotypes also had a higher cell membrane thermostability and higher Fv/Fm under high temperature conditions. Among the analysed traits, it can be concluded that CMS and Fv/Fm can be used efficiently to screen the germplasm for thermotolerance.

Identification of effective inoculum of Rhizoctonia solani (Kuhn) for screening of Wa-Male-Sterile lines in rice against sheath blight disease

Occurrence of sheath blight disease (Rhizoctonia solani Kuhn) in rice (Oryza sativa L.) is a regular feature in tropical South Asia and causes huge economic losses. Till now, no resistant cultivar has been developed against the pathogen and gene(s) conferring complete resistance for the disease are not reported in the available rice germplasm. This necessitates the screening of new rice germplasm against the pathogen to identify the resistance source. Ten newly developed Wild Abortive (WA) cytoplasmic male-sterile (CMS) lines, along with a susceptible cultivar (cv. Pant Dhan-4) were evaluated under green-house conditions in a randomized complete block design, with three replications. Screening was done using fungal mycelia disc (15 mm size diameter) and sclerotia (0.2 mg) to determine the potentiality of inoculum. Genotypes were assessed for total lesion length (cm) at 3, 6, 9 and 12 days after inoculation. The response in relative lesion length varied significantly depending upon sclerotia or mycelium discs used and genetic background. During initial period of disease development, non-significant variation was observed but later on the response of genotypes was clearly distinguishable when lesion size gradually increased. Disease severity index was comparatively higher for sclerotial inoculation than mycelial inoculation indicating sclerotia are more effective. The genotype UPRM 271-8-5EUI-3-2A showed the lowest severity in both the methods of inoculation. The highest severity was recorded for UPRM 78-4-1A (mycelial inoculation) and UPRM 271-8-5EUI-6-4A (sclerotial inoculation). Disease appearance was more uniform and higher in sclerotial inoculation when compared with mycelial inoculation. Screening of rice germplasm using uniform sized sclerotia and disease assessment at one week after inoculation were found to be the most effective for screening of rice cultivars.

Flanking SSR markers for allelism test for the Asian rice gall midge (Orseolia oryzae) resistance genes

Screening of rice germplasm against Asian rice gall midge, Orseolia oryzae (Wood-Mason), biotypes in India has led to identification of over 300 resistant rice genotypes. However, only ten resistance genes have been characterized so far. Identification of new genes through classical allelism test is tedious and time consuming. We propose to use closely linked flanking Simple Sequence Repeat (SSR) markers in allelism tests for identification of resistance genes. Of the ten known gall midge resistance genes, eight have been tagged and mapped. The Gm1 and Gm2 genes have closely linked flanking markers. Hence SSR markers RM219 and RM444, flanking the gene Gm1, and RM317, RM241 along with the SCAR marker F8, flanking the gene Gm2, were selected for this study. Tests with one set of 13 genotypes likely to carry Gm1 and another set of 17 genotypes suspected to contain Gm2 suggested the presence of the respective allele in all the 13 and 15 genotypes from these sets, respectively. Classical allelism test perfectly matched with the markers test. There were two exceptions involving amplification with RM444 in cultivar Kavya and with RM241 in genotype AE20, suggesting a single recombination which could have resulted in the mismatch. All the three markers in the genotype Bhumansan and the two flanking markers RM317 and F8 in AE20 indicated the absence of the Gm2 allele. This was validated through a classical test, revealing a segregation ratio of 15 resistant: 1 susceptible F2 progeny of both the crosses between the Gm2 source Phalguna and these genotypes. We performed the allelism test with the markers on another set of 56 randomly selected gall midge resistant genotypes to discover possible sources of new resistance genes.

The screening of rice germplasm, including those transgenic rice lines which accumulate β‐carotene in their polished seeds, for their carotenoid profile

A large number of exotic and commercial rice cultivars were screened to explore the carotenoid profile of the rice germ plasm. The data were compared with that of some transgenic plants where the genes for the entire biochemical pathway used to synthesize β-carotene had been engineered into the plant in such a way that it was hypothesized that β-carotene would be detectable in polished seeds, when normally polished seeds do not contain β-carotene. Eighty-eight rice accessions were used for the screening; 79 were obtained from the germ plasm bank of the International Rice Research Institute in the Philippines. Nine cultivars (Basmati 370, BR28, BR 29, BR-R, Kranti, Limpopo, Mahsuri, NDR359 and Pantdhan4) from other countries were also included. Among the 88 non-transgenic rice accessions (including BR-R, an elite restorer line), 69 cultivars were screened, using both polished ad unpolished samples and 19 cultivars were screened for unpolished seeds only. Forty-nine cultivars (unpolished) were analysed using the 85-min HPLC system, whereas 40 accessions (polished and unpolished) were run using the 30 min HPLC method. None of the polished cultivars were identified as containing β-carotene when both HPLC conditions were used. When unpolished, a majority of the rice accessions showed both lutein and β-carotene. Chlorophyll and other unidentified peaks were eluted between lutein and β-carotene in immature seeds. Transgenic rice contained not only β-carotene and lutein but also other carotenoids after polishing.