Image: Vespertunes via Wikimedia Commons
Endophytes are microbes that grow inside plant tissues. They are not infectious but have a symbiotic relationship with the plants they inhabit. Some endophytes help growth and reproduction while some others help ward off pathogens and pests.
Seeds of different rice cultivars harbour a wide range of endophytes. Can seed-transmitted endophytes increase the growth indices of rice? Researchers from IIT Kharagpur investigated.
The team collected the mature seeds of two aromatic rice cultivars – Kalonunia and Dehradun Basmati. They sterilized and cultured the seeds in suitable media to grow the callus – an unorganized mass of cell growth. Some of the cultured calli grew roots and shoots.
The researchers ground the in vitro grown rice tissues and spread the extracts on different bacterial media to isolate any endophytic bacteria present. They could isolate bacteria only from calli.
The team identified nine types of endophytes from the two aromatic rice cultivars. Eight were Gram-negative and rod-shaped. One was a Gram-positive cocci-shaped bacteria. Molecular screening of the nine isolates showed that they belonged to four genera: Methylrubrum, Pseudomonas, Micrococcus, and Methylobacterium.
The researchers employed a battery of tests and found that the endophytes enhance nitrogen fixation, and ammonia and siderophore production in the two cultivars.
But can endophytes of one variety be used to prime another type for better harvest?
The team used all nine endophyte isolates for seed priming. Besides the seeds of the two aromatic cultivars, they also primed the seeds of IR64, a widely grown normal rice cultivar.
“Compared to unprimed control seeds, primed seeds grew better – there was a notable increase in biomass in primed seeds in all three cultivars”, says Anagha Krishnamoorthy, IIT Kharagpur.
Then, the team primed IR64 rice seeds with Pseudomonas fluorescens, an established microbe used for priming. They compared results. After a fortnight, growth indices improved in all primed seeds.
“When we did microscopic analysis of root tissues, we found an increase in both cell number and cell growth in all cultivars primed with the endophytes, ”, says Adinpunya Mitra, IIT Kharagpur.
The IR64 cultivar primed with the bacterial endophytes showed an increase in plant height, chlorophyll content, and grain production.
“Priming seeds with endophytes improves rice productivity,” says Tapas Kumar Maiti, IIT Kharagpur.
Are seed companies listening?
Microbiological Research, 241: 126582 (2020)
K. Sri Manjari
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