Investigations on yellowing of black pepper (piper nigrum L.)
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Date
2019
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Department of Plantation Crops and Spices, College of Horticulture, Vellanikkara
Abstract
Black pepper, popularly known as King of Spices or Black gold is one of the important and earliest known spices produced and exported from India. After foot rot disease, the major constraint in black pepper cultivation is the incidence of yellowing, leading to decline in production year after year. Yellowing is reported to be caused by many abiotic and biotic factors. Symptomatological studies on yellowing showed that per cent severity of yellowing was significantly higher during October-November and was on par during summer. During July-August, yellowing was significantly low. There was no definite pattern in the development and spread of the disease. In case of mild yellowing, there was recovery during July-August. Yellowing gradually increased and severely affected plants failed to recover. There was no flushing or flowering in plants. Such plants died in 2-3 years. All varieties studied were found to be susceptible to yellowing. Yellowing was observed either at the top of pepper column or (and) the bottom of the column. Sometimes yellowing appeared in a group of leaves together. In some aged plants older leaves at terminal portion of plant were yellow. In some leaves the base of lamina near petiole was yellow. This yellowing faded to tip of lamina and margins. Yield and yield contributing characters in healthy, apparently healthy and yellowing affected black pepper plants showed that all the characters of healthy plants showed a higher positive value compared to yellowing affected plants. In the case of yield per plant, there was significant reduction in yield in yellowing affected plants compared to healthy in all varieties except Vijay. In the study on rhizosphere soil nutrient status there was no apparent role of soil pH, OC, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu and B in causing yellowing in the experimental plots in the present study. All the nutrient elements were in the optimum
or high range. There was no significant difference among yellowing affected, apparently healthy and healthy plants in case of N and S where DRIS norms were not available. Among the rhizosphere soil parameters, pH, EC and organic carbon were significantly and positively correlated with yellowing. There was no significant correlation of N, P, Mg, S, Fe, Mn, Zn, Cu and B content of rhizosphere soil with yellowing in black pepper. K, Ca and Al content of rhizosphere soils showed significant negative correlation with yellowing. Analysis of nutrient status in the plant tissues of yellowing affected, apparently healthy and healthy plants based on DRIS norms suggested by Hamza et al. (2007) indicated that there was deficiency of N in the yellowing affected plants, K content and S content was also low in yellowing affected plants, all other nutrients were not deficient in the yellowing affected plants. Study on soil micro flora (cfu g-1) showed that mean value of fungal population was significantly highest (18.78 ×10 3cfu g-1) in rhizosphere soils of healthy plants compared to apparently healthy and yellowing affected plants. Healthy plants showed significantly low (27.55 ×10 3cfu g-1) population count of actinomycetes in the rhizosphere soil, whereas apparently healthy and yellowing affected plants were statistically on par. Yellowing affected plants showed significantly highest population count of bacteria (25.53 ×10 8cfu g-1) followed by apparently healthy. Healthy plants showed significantly lowest bacterial population. No soil borne pathogens including Phytophthora, Rhizoctonia or Fusarium was found associated with yellowing Nematode population in the rhizosphere soils of healthy plants was significantly lowest compared to apparently healthy and yellowing affected plants. Yellowing affected plants showed significantly highest population of Meloidogyne incognita, Radopholus similis, Pratylenchus sp, Helicotylenchus sp, Dorylaimid sp,
and Trophotylenchulus sp, in the rhizosphere soil when compared with apparently healthy and healthy plants. In case of root, number of galls on the roots was significantly highest in yellowing affected plants. Considering different categories of nematodes, Meloidogyne incognita followed by Radopholus similis were predominant in the roots of yellowing affected plants. In roots as well as rhizospere soil, significantly highest population of nematodes was observed during October – November followed by February – March. Examination of roots of experimental plants and rhizosphere soil did not show the presence of root mealy bugs or any other insect, which can cause damage to root or yellowing in the plant. There was significant positive correlation of yellowing with maximum temperature. However minimum temperature showed significant negative correlation with yellowing. Relative humidity and rainfall also were significantly and negatively correlated with yellowing. A definite association of plant parasitic nematodes was seen in the plants as well as rhizosphere soils of yellowing affected plants in the present study. Meloidogyne incognita followed by Radopholous similis population was significantly highest in yellowing affected plants indicating their role clearly in causing yellowing. In the present study on the analysis of different factors like soil nutrients, plant pathogenic micro-organisms, soil borne insects, nematodes etc, in causing yellowing gives a clear indication of role of nematodes in causing yellowing in black pepper in the experimental plot in Thrissur district. Even though the nutrient status in the rhizosphere soil of experimental plants was satisfactory, absorption of nutrients was low due to damage of roots caused by nematodes. There was deficiency of nitrogen and low potassium and sulphur levels in the leaves of yellowing affected plants. The yellowing expressed must be due to multiple factors and combined effect of multiple nutrient deficiencies in plant tissue and damage due to nematodes
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174736