(i) Tungro Virus:

Rice tungro baeilliform virus was first described by Saito (1975). The role of RTBV as a member of the virus complex causing tungro disease Rice tungro baeilliform virus (RTBV) is a plant pathogenic virus of the family Caulimoviridae. Tungro means ‘degenerated growth’ and was first observed in Philippines.

Galves (1968) purified the virus and reported that the particles are polyhedral with a diameter of 30-33 nm. The virus withstands temperatures below 63 degree celsius for 10 minutes. Tungro affected rice plants are stunted and have reduced number of tillers. The young emerging leaves develop interveinal chlorosis leading to discoloration of the leaves, starting from tip downwards.

Often whole leaf is discolored plants infected at an early stage generally die prematurely. Infected plants take more time for maturity because of delayed flowering. The panicles are often poorly developed and the grains are also often covered with dark brown blotches and are lighter than those of healthy plants.

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The tungro virus is known to have at least two strains – S and M. The ‘S’ strain in these varieties produces conspicuous interveinal chlorosis, giving an appearance of yellow stripe and sometimes irregular chlorotic specks on younger leaves. On the other hand, the ‘M’strain produces only mottling.

(ii) The concept of phytocyanide:

Phytoncides are antimicrobial allelochemic volatile organic compounds derived from plants. The word, which means “exterminated by the plant”, was coined in 1937 by Dr. Boris P. Tokin (1900-1984), a Russian biochemist from Leningrad University. He found that some plants give off very active substances which prevent them from rotting or being eaten by some insects and animals.

Various spices, onion, garlic, oak and pine trees (and bark) and many other plants give off phytoncides. The major ingredient of Phytoncide is very volatile terpene with a number of other ingredients contained. Many scholars think that the emergence of SARS that caused the world trembled has deep relationship with the destruction of the forests in the Kuangdong area of China.

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The air in the place where there is no forest and tree is no longer living air. The destruction of forest means the lose of Phytoncide. Phytoncide controls or kills various germs and viruses in air, purifies the air and enhances the self-cleaning capability.

Phytoncide has been keeping the health of mankind in invisible places. As the respiratory diseases and mutant virus have become worldwide issue, and various syndromes caused by the chemical substances become more serious problems in reality, the interests on Phytoncide will be magnified even more.

More than 5000 volatile substances defend the surrounding plants from bacteria, fungi and insects. Phytoncides work by preventing the growth of the attacking organism. These facts explain partially why feral bees that live in forest are healthy!

The idea of walking in the woods has been developed in Europe in the mid-nineteenth as a certain part of recreational activity. In Taiwan, South Korea and Japan, people commonly engage in so-called forest(or woods) bathing to breathe in phytoncides emitted by plant and trees, in order to improve their health. The physiological effects of phytoncide have been investigated in biomete,prological research (Japanese Society of Biometeorology, 1992).