Microbiome for sustainable agriculture: a review with special reference to the corn production system.

Microbial diversity formed by ages of evolution in soils plays an important role in sustainability of crop production by enriching soil and alleviating biotic and abiotic stresses. This diversity is as an essential part of the agro-ecosystems, which is being pushed to edges by pumping agrochemicals and constant soil disturbances. Consequently, efficiency of cropping system has been decreasing, aggravated further by the increased incidence of abiotic stresses due to changes in climatic patterns. Thus, the sustainability of agriculture is at stake. Understanding the microbiota inhabiting phyllosphere, endosphere, spermosphere, rhizosphere, and non-rhizosphere, and its utilization could be a sustainable crop production strategy. This review explores the available information on diversity of beneficial microbes in agricultural ecosystem and synthesizes their commercial uses in agriculture. Microbiota in agro-ecosystem works by nutrient acquisition, enhancing nutrient availability, water uptake, and amelioration of abiotic and abiotic stresses. External application of such beneficial microbiota or microbial consortia helps in boosting plant growth and provides resistance to drought, salinity, heavy metal, high-temperature and radiation stress in various crop plants. These have been instrumental in enhancing tolerance to diseases, insect pest and nematodes in various cropping system. However, studies on the microbiome in revolutionary production systems like conservation agriculture and protected cultivation, which use lesser agrochemicals, are limited and if exploited can provide valuable input in sustainable agriculture production.

Genetically modified crops: current status and future prospects.

MAIN CONCLUSION: While transgenic technology has heralded a new era in crop improvement, several concerns have precluded their widespread acceptance. Alternative technologies, such as cisgenesis and genome-editing may address many of such issues and facilitate the development of genetically engineered crop varieties with multiple favourable traits. Genetic engineering and plant transformation have played a pivotal role in crop improvement via introducing beneficial foreign gene(s) or silencing the expression of endogenous gene(s) in crop plants. Genetically modified crops possess one or more useful traits, such as, herbicide tolerance, insect resistance, abiotic stress tolerance, disease resistance, and nutritional improvement. To date, nearly 525 different transgenic events in 32 crops have been approved for cultivation in different parts of the world. The adoption of transgenic technology has been shown to increase crop yields, reduce pesticide and insecticide use, reduce CO2 emissions, and decrease the cost of crop production. However, widespread adoption of transgenic crops carrying foreign genes faces roadblocks due to concerns of potential toxicity and allergenicity to human beings, potential environmental risks, such as chances of gene flow, adverse effects on non-target organisms, evolution of resistance in weeds and insects etc. These concerns have prompted the adoption of alternative technologies like cisgenesis, intragenesis, and most recently, genome editing. Some of these alternative technologies can be utilized to develop crop plants that are free from any foreign gene hence, it is expected that such crops might achieve higher consumer acceptance as compared to the transgenic crops and would get faster regulatory approvals. In this review, we present a comprehensive update on the current status of the genetically modified (GM) crops under cultivation. We also discuss the issues affecting widespread adoption of transgenic GM crops and comment upon the recent tools and techniques developed to address some of these concerns.

Expression of cry1Aa gene in cabbage imparts resistance against diamondback moth (Plutella xylostella).

Brassica oleracea cv. Pride of India is one of the most promising vegetable cultivars commercially grown as cash crop in Himachal Pradesh, India. However, its overall production is severely hampered by diamondback moth (Plutella xylostella), a notorious pest. To avoid yield losses caused by this pest, cryIAa gene was introduced into cabbage cv. Pride of India using Agrobacterium-mediated transformation method. In an attempt to maximize the transformation frequency, critical determinant factors such as explant type, pre-incubation and co-cultivation period, and acetosyringone effect were successfully optimized. The highest transformation frequency (4.67% and 14.50%) in cotyledon and hypocotyl explant was achieved with a pre-incubation period of 72 h and co-cultivation period of 48 h. Furthermore, transformation frequency was enhanced in cotyledon (18.66%) and hypocotyl (32.00%) explants, when selective regeneration medium was fortified with 100 µM acetosyringone, respectively. The transgene (cryIAa) integration and copy number were confirmed using PCR and Southern blotting. Reverse transcriptase PCR and quantitative real-time PCR analyses were performed that proved transcriptional expression of cryIAa gene in PCR-positive transgenic events. Transgenic cabbage-fed diamondback moth larvae showed significantly higher mortality, thereby proving transgene effectiveness against insect pest control.

Development of transgenic broccoli with cryIAa gene for resistance against diamondback moth (Plutella xylostella).

Transgenic broccoli (Brassica oleracea L. var. italica) cv. 'Solan Green Head' has been developed by using Agrobacterium tumefaciens strain harboring cryIAa gene for resistance against diamondback moth (Plutella xylostella). By combining the best treatments of 72 h pre-culturing and 48 h co-cultivation time period, a transformation frequency of 4.92 and 13.83% was obtained from cotyledon and hypocotyl explants, respectively. Supplementing the co-cultivation medium with acetosyringone in a concentration of 100 µM enhanced the transformation frequency to 17.92 and 32.11% in cotyledon and hypocotyl explants, respectively. The transgene (cryIAa) integration was confirmed by polymerase chain reaction using gene-specific primers and Southern blot analysis using digoxigenin nonradiolabelled DNA probe. Gene expression in the PCR-positive transgenic events had been confirmed by reverse transcriptase-PCR and quantitative real time-PCR. Insect bioassay proved the effectiveness of the transgene against infestation by diamondback moth (Plutella xylostella) larvae. To the best of our knowledge, this is the first report of optimization of a highly efficient transformation system and transgenic development in broccoli using cry1Aa gene for insect resistance.

Assessment of genetic diversity in lettuce (Lactuca sativa L.) germplasm using RAPD markers.

The importance of germplasm characterization is an important link between the conservation and utilization of plant genetic resources in various breeding programmes. In the present study, genetic variability and relationships among 25 Lactuca sativa L. genotypes were tested using random amplified polymorphic DNA (RAPD) molecular markers. A total of 45 random decamer oligonucleotide primers were examined to generate RAPD profiles, out of these reproducible patterns were obtained with 22 primers. A total of 87 amplicon were obtained, out of which all were polymorphic and 7 were unique bands. The level of polymorphism across genotypes was 100% as revealed by RAPD. Genetic similarity matrix, based on Jaccard's coefficients ranged from 13.7 to 84.10% indicating a wide genetic base. Dendrogram was constructed by unweighted pair group method with arithmetic averages method. RAPD technology could be useful for identification of different accessions as well as assessing the genetic similarity among different genotypes of lettuce. The study reveals the limited genetic base and the needs to diversify using new sources from the germplasm.

High frequency regeneration of plants from cotyledon and hypocotyl cultures in Brassica oleracea cv. Pride of India.

Morphogenic potential of cabbage cv. Pride of India, for multiple shoot induction was tested under in vitro conditions using cotyledon and hypocotyl explants. Aseptically grown seven to nine days old seedlings of cabbage were used as source of explants for reproducible plant regeneration studies. Forty different concentrations and combinations of TDZ (alone), TDZ with adenine, TDZ with NAA and TDZ with IAA were tried. Maximum shoot regeneration response from cotyledon explants (91.11%) and hypocotyl (94.40%) was obtained on MS medium containing 0.330 mg/l TDZ + 79.70 mg/l Adenine and 0.220 mg/l TDZ + 0.088 mg/l IAA, respectively. Rooting was achieved within two to three weeks on all the rooting media, but MS medium containing 0.10 mg/l NAA produced the maximum number of strong and healthy roots (100%). The regenerated complete plantlets with healthy roots and shoot system were transferred to pots containing sterilized cocopeat and successfully acclimatized and no phenotypic variations were observed among regenerated plants. Highly efficient, reproducible plant regeneration protocol has been standardized in cabbage cv. Pride of India, which would be valuable for Agrobacterium-mediated gene transfer studies in cabbage.