EVALUATION OF A FEW BOTANICALS AND BIOAGENTS IN SEED TRANSMISSION OF BROWN SPOT OF RICE CAUSED BY BIPOLARIS ORYZAE
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Date
2019-07
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AAU, Jorhat
Abstract
Brown spot of rice caused by Bipolaris oryzae Subr. and Jain (syn. Helminthosporium oryzae Breda de Haan) is an important disease of rice which has been reported to occur in all the rice growing countries of the world. In India, it is known to occur in all the rice growing states including Assam causing loss of 5-53.33 percent annually. Considering its widespread significance, an experiment was conducted to study the effect of a few botanicals and bioagents in seed transimission of the disease. The location of B. oryzae in the rice seed and its transmission from seed to seedling were studied. Each part of infected seed including embryo, endosperm, lemma, palea, sterile lemma and rachilla, was found to be infected by B. oryzae. The highest level of infection was found in endosperm (78.50 percent) followed by rachilla (68.50 percent). Lowest infection was found in embryo (32.50 percent).Transmission studies from the infected seed to the seedling using test tube agar, blotter and sand indicated that primary symptom appeared on coleoptile and roots after 7 – 14 days. However, recovery of infection percentage was greater in test tube agar and blotter than sand method. Efficacy of three botanicals viz., Turmeric (Curcuma longa), Neem (Azadirachta indica), Tulsi (Ocimum sanctum) in different concentrations (10%, 20% and 50% each in Turmeric in Neem and 20%, 30% and 50% in Tulsi) and one bioformulation, Biogreen @5%, 10% and 15% concentration was studied to reduce growth of B. oryzae in vitro and its transmission from treated seeds to seedlings. Turmeric @50% concentration was found to be most effective in reducing the colony growth of the pathogen (1.97 cm and 72.87 percent inhibition over control) followed by Turmeric 20% concentration (3.16 cm and 56.47 percent inhibition over control), Tulsi 50% and Biogreen 15% concentration (3.52 cm and 3.84 cm respectively). Turmeric 50% and Turmeric 20 % concentration were also the most effective in reducing the transmission of the pathogen from seed to seedling both in test tube agar method and sand method. These four treatments from the in vitro experiments were further studied for their effect on seed transmission of B. oryzae, Percent Disease Incidence (PDI) and seed quality parameters under pot condition. Percent Disease Incidence was found to be the lowest in the treatment Turmeric @50% during all the three observed stages (8.36, 9.58 and 18.54 percent at Tillering, Panicle Initiation and Grain filling stage respectively). At grain filling stage Turmeric @50% was followed by Tulsi @50% (19.44). However at this stage PDI observed in treatments Tulsi @50%, Turmeric @20% (22.71) and Biogreen @15% (24.59%) were at par with each other. Seed yield per plant was highest in the treatment Turmeric @50% (29.40 g) which was at par with that of Carbendazim @0.2% (28.80 g) and Turmeric 20%(28.52 g). Thousand seed weight was also highest in the treatment Turmeric @50% (22.48 g) followed by control treatment (Carbendazim @0.2%) (21.86 g). Seedling vigour and speed of germination were significantly higher in the treatment Turmeric @50% (1244.37 and 10.79 respectively) but germination percentage of the treatment Turmeric @50% (92.50%) was at par with that of treatment
Turmeric @20% (89.00%) and Carbendazim @0.2% (93.50%). Mean germination time
was also significantly lower in the treatment Turmeric @50% (4.74 days). Mean daily
germination was found to be highest in the treatment Turmeric @50% (3.49) which is
statistically at par with the treatment Turmeric @20% (3.46) and Carbendazim @0.2%
(3.44).
The harvested seeds from different treatments showed varying level of
association by B. oryzae. Seeds in Agar plate method showed infection of 25.75 percent
and 37.72 percent reduction over absolute contol in the treatment Turmeric @50%
which was lowest among botanicals and bioagents. The treatment Carbendazim @0.2%
was the best in all the observed parameters. However, seed yield per plant, germination
percentage, mean daily germination and mean germination time were at par with those
of the treatment Turmeric @50% concentration.