Management of Citrus Decline Disease Using Biological Technique

Abstract

Citrus reticulate is a major economic crop in Thailand. Chiang Mai in northern Thailand famous for the production of high quality mandarin citrus cultivar called Sainamphung. However, the plantations are being damaged by diseases such as, citrus decline disease, which causes the reduction of the harvest. Currently the farmers do not have proper knowledge and skills for crop management to solve this problem. From the preliminary survey regarding four plots among Chai Prakan, Fang and Mae Ai districts in Chiang Mai province, it was found that in Pang Seaw, Sithawong, Phu Meun and Somkait orchards shown the symptoms of citrus decline disease. From the assessment of these orchards, it was found that, the severity of the disease depends on the management of plantation, age, citrus tree, soil condition, water, environment, weather and the use of various agricultural chemicals. According to the survey of citrus root rot in above four plots, all the symptoms were found with different severity levels. The most severe symptoms were found in the crescent garden and Suan Pu Muen. Among the 64 isolates, 37 isolates were belonged to phytophthora and 27 isolates of Pythium. In the pathogenicity test under the laboratory conditions, with the detached leave method and seedling test method, 60% of all infections caused the disease with varying severity levels. Citrus leaves were collected randomly from Pang Seaw, Phu Muen and Sithawong. The leaves with unusual symptoms including yellow leaves, green leaves, slender leaves, thin leaves, hard leaves and rough leaves were tested using Polymerase Chain Reaction for the greening caused by Liberibacter asiaticus. Among the 10,000 of leaves collection from Pang Siang Park, 95.83% of specimens did not show any symptom. Highly diverse symptoms of greening was shown by 87.50% of the infections. As the main symptom, the leaf turns yellow until pale and clear pattern was not shown. The centre line leaves and branches are dark green. Most of the symptoms are found in young leaves. The leaves are smaller and thicker than usual. In addition, bacteria can become latent in the leaves. The infection was spread throughout the experimental areas in Both Pang Seaw (3-4 years trees) and Phu Muen and Sithawong (more than 10 years trees). The observations have shown that the infection has been developed in the area for a long time. Which allowed the disease to spread over the seedlings through seeds and shoot cuttings. Therefore, the results of the test concluded that the cause of decline stem disease in tangerine was caused by the Liberibacter asiaticus, Phytophthora and Pythium. In the crescent garden, High amount of lime stones effects the soil quality and drainage, and showed the most severe decline symptoms. The study focus on antagonistic microorganisms for the biological control of the citrus decline disease. Antagonistic microorganisms were isolated and tested against the root rot disease in laboratory conditions. The antagonistic fungus Chaetomium spp. was isolated from Chiang Mai Province. Fungi were isolated from 28 samples. Chaetomium spp. Isolates CP3 and HT1 CP2 showed the best inhibitory effect against Phytophthora and Pythium. Controlling citrus decline disease (root rot, stem rot and greening) in greenhouse condition by planting tangerine seedlings which were propagated by means of a one-year-old cutting stock. The cuttings were divided and gave 12 treatments to compare the bio controlling of greening and root rot diseases. The use of organic fertilizers to improve soil quality together with Chaetomium spp. and the management of the farmers' practice emphasizing the use of chemical fertilizers both soil and foliar by measuring the growth of citrus trees in pots including the number of new shoots, length, peak, height of the citrus tree. The amount of chlorophyll in the citrus leaf, the size of the citrus leaf and the amount of citrus root for 8 months was found that the management using bio-technique and farmers’ management causing the citrus trees grown in both types of diseases to grow that are not different. The organic fertilizers together with Chaetomium fungi were used to improve the soil quality of the citrus plantations in Phu meum Som Kiat Suan Pang Seaw and Suan Sithawong. The effects of the treatment was assessed through, severity of the disease, growth parameters of the tree including the number of new shoots, length, amount of chlorophyll in the leaf, leaf size, number of fruits, size of the fruits, sweetness and the yield for 11 months. The test was designed to investigate the biological control of Citrus Decline Disease. Further the use of organic fertilizers to improve soil quality together with the use of Chaetomium fungi in the citrus Phu meum Som Kiat Suan Pang Seaw and Suan Sithawong was also tested. The The severity of the disease, the growth of citrus trees including the number of new shoots, length, amount of chlorophyll in the leaf, leaf size, number of fruits, sweetness and yield for 11 months. Blade and the effects were not different in both methods of management in each garden. The results of the fruit size showed that Pang Siang Park, Sittiwong Garden and Suan Som kait had different sizes of citrus fruits in each process. Further, the citrus flesh in the process using chemical fertilizer has a decaying area, and a larger number of seeds in Suan Phu Muen, the process of using chemical fertilizers has a larger effect. But when comparing the sweetness, it was found that the plants treated with the organic fertilizers togather with Chaetomium spp. are sweeter than the plants treated with chemical fertilizer, except for the crescent garden. due to the lack of production corresponds to the tests in the green house. Therefore, biotechnology can be another option for farmers to reduce the use of chemical fertilizers to maintain long-term soil quality.