EFFECT OF INTEGRATED DISEASE MANAGEMENT PACKAGES ON DISEASES INCIDENCE AND BULB YIELD OF ONION ( Allium cepa L . )

A field experiment was conducted to find out the effect of different integrated disease management (IDM) packages on severity of basal rot (Fusarium oxysporum), white rot (Sclerotium rolfsii) and stemphylium blight (S. vesicarium) diseases, and bulb yield of onion (Allium cepa L.) variety Agrifound Light Red. Nine IDM packages consisting of NPK fertilizers, farm yard manure, biocontrol agents and spray of fungicides starting from 30 days of transplanting at 15 days interval were applied. The incidence of basal rot and white rot of onion bulbs ranged from 0.984.31% and 0.00-0.96%, respectively. The highest incidence of basal rot (4.31%) and white rot (0.96) was recorded in bulbs harvested from untreated control. The lowest incidence of basal rot (0.98%) was found in bulbs harvested from the IDM package consisting of NPK @ 100:50:50 kg ha + FYM @ 10 t ha + vermicompost @ 1 t ha + Ps. fluorescens @ 5 kg ha + copper oxychloride @ 0.3%). White rot did not appear under this package. The lowest Stemphylium blight intensity (3.87%) was achieved with the package having four foliar sprays of propiconazole @ 0.1% followed by mancozeb @ 0.25% and copper oxychloride @ 0.3%. The IDM package increased the bulbs yield over standard check by 25.54% and over untreated control by 109.42%. The average highest bulb diameter (54.15 mm) and bulb size index (23.27 cm) and lowest incidence (0.98%) of basal rot disease in onion bulbs was also obtained with IDM package consisting of NPK @ 100:50:50 kg ha + FYM @ 10 t ha + vermicompost @ 1 t ha + Ps. fluorescens @ 5 kg ha + copper oxychloride @ 0.3%).


INTRODUCTION
Onion (Allium cepa L.) is an exportable bulb crop among the cultivated Allium species in India.The country is a traditional exporter of fresh onion with 67% share of the total export of fresh vegetables.Onion is exported to the Iran, UAE, Malaysia, Bangladesh, Sri Lanka, Indonesia, Vietnam, Reunion France and Singapore (Anonymous 2008).Onion is cultivated in summer (Rabi), rainy (Kharif) and dry periods (late Kharif) seasons in the country and maximum area under cultivation is being covered in Rabi season.India ranks second in cultivated area as well as onion production in the world.It has been estimated that more than 25% yield losses occur due to foliar diseases, especially Stemphylium blight (S. vesicarium) and purple blotch (Alternaria porri).Onion crop also suffers from basal rot (Fusarium oxysporum) and white rot (Sclerotium rolfsii) diseases causing various extents of losses (Entwistle, 1990).About 30-40% storage losses in onion occur due to incidence of Fusarium basal rot (Gupta et al., 2008;Barnoczkine, 1986).The diseases are also responsible for deterioration of export quality of onion bulbs (Gupta et al., 2009).
Trichoderma viride and Pseudomonas fluorescens have antagonistic capacity against plant pathogens which enhance systemic acquired resistance and plant growth promoting character.Pseudomonas fluorescens plays an important role in phosphate solubilization which improves the soil and plant health.Scanty information is available on quality production of onion by approaching integrated crop health and disease management (Gupta et al., 2009).Gupta et al., (2008) conducted in-vitro study for the management of soil borne fungal pathogens like Fusarium oxysporum and Sclerotium cepivorum using bio agents and oil cakes and findings indicated that T. viride inhibited 50.74% mycelia growth as well as 93.59% inhibition in sclerotia production of S. cepivorum while 70.40% inhibition in mycelia growth of F. oxysporum.Gupta et al. (2011) reported that basal rot and white rot in onion can be managed by the application of Trichoderma viride, T. harzianum and Pseudomonas fluorescens.In view of the above facts, the present study was undertaken to find out the effect of different IDM packages on severity of soil borne and foliar diseases, and yield of onion.
All the recommended intercultural practices were followed to grow the crop.Irrigation was applied at regular intervals to maintain the optimum moisture level in the field.The crop was harvested at bulbs maturity.The incidence and intensity of basal rot and white rot of bulbs were recorded after harvesting based on the covering area of infected bulb by the fungal pathogen following 0 to 5 scales.The severity of Stemphylium blight was indexed at 30, 45, 60 and 75 days after transplanting on a 0-5 scale and Percent Disease Index (PDI) was computed (Sharma, 1995).Data on incidence and intensity of basal rot and white rot disease of onion bulbs, exportable bulb yield, gross yield and bulb size were recorded after harvest.The data recorded in two consecutive years were pooled and analyzed statistically by Randomized Block Design.The cost benefit ratio was also computed.

Incidence of basal rot and white rot diseases
The incidence of basal rot and white rot diseases in onion bulbs ranged from 0.98-4.31%and 0.00-0.96%,respectively.The highest incidence of basal rot as well as white rot was recorded in bulbs harvested from untreated control.The lowest incidence of basal rot (0.98%) was found in bulbs harvested from the treatment T 4 (NPK @ 100:50:50 + FYM @ 10 t ha -1 + vermicompost @ 1 t ha -1 + Ps. fluorescens @ 5 kg ha -1 + copper oxychloride @ 0.3%).White rot did not appear under this treatment (T 4 ).However, the lowest incidence of the disease (0.18%) was recorded from T 5 (NPK @ 100:50:50 kg ha -1 + FYM @ 20 t ha -1 + T. viride @ 5 kg ha -1 + seedling root dip (10g T.viride+100g FYM + 1 liter water + spray of propiconazole at 0.1%).It was found that soil application of Ps. fluorescens and Trichoderma viride supplemented with root dip method effectively control the soil borne fungal disease of onion.The data presented in figure 4 revealed that 100% control of white rot disease and maximum control of basal rot disease were obtained with the application of Ps. fluorescens @ 5 kg ha -1 in the soil in treatment T 4 as compared to the untreated control.The present study revealed that Ps. fluorescens was most effective against soil borne disease of onion followed by T. viride (Table 1).
Data presented in figure 4 revealed that 100% control of white rot and basal rot of onion bulb was obtained with soil application of Ps. fluorescens @ 5kg ha -1 followed by T. viride @ 5 kg ha -1 as soil application as well as seedling root dip (10g T.viride+100g FYM + 1liter water) compared to the results of the present study reveal that Ps. fluorescens and T. viride is most effective against soil borne diseases of onion.Rajendran and Rangnathan (1996) reported that soil application of T. viride and other species were effective against basal rot (Fusarium oxysporum) pathogen.Other workers also reported that biocontrol agents such as T. viride, Gliocladium zeae and Coniothyrium minitans gave effective control of white rot disease of onion caused by Sclerotium rolfsii (Gupta et al., 2011;Ahmad and Tribe, 1977).
Propiconazole @ 0.1% was most effective against foliar diseases as well as increasing the onion bulb yield and could be recommended as curative measure against Stemphylium blight as an ad-hoc decision making component of integrated disease management strategy (Table 2).
The data presented in figure 3 revealed that the highest control of Stemphylium blight intensity (62.21%) of onion was achieved with foliar sprays of propiconazole @ 0.1% followed by mancozeb @ 0.25% (55.63 and copper oxychloride @ 0.3% (54.78%).The results of the present study reveal that propiconazole was the most effective against Stemphylium blight followed by mancozeb and copper oxychloride.Gupta et al. (1996) reported that spray of contact fungicide mancozeb @ 0.25% reduced the incidence and intensity of Stemphyllium blight in onion.Foliar spray of mancozeb @ 0.25 % was also recommended by some other workers for the control of foliar diseases of onion like Stemphyllium blight and purple blotch (Alternaria porri) of onion (Borkar and Patil, 1995;Srivastava et al., 1999;Mathur and Sharma, 2006;Gupta et al., 2011a & b).Mathur and Sharma (2006) reported that spraying of mancozeb @ 0.2% and copper oxychloride @ 0.3% thrice at 15 days intervals significantly superior in reducing purple blotch and Stemphylium blight as well as increasing the yield of onion bulbs.Gupta and Pandey (2011) conducted a field study on management of foliar diseases of onion and reported that propiconazole and mancozeb sprays at 15 days intervals effectively controlled the foliar diseases of onion.
Figures 1 and 2 show that, remarkably higher exportable yield of onion bulbs was observed in integrated nutrient applying chemical fertilizers along with organic manures (T 4 ) which caused an increase of 25.44% over recommended doses of NPK fertilizers (standard check) and 109.42% over untreated control.
The findings of the present study revealed that judicious use of fertilizers, organic manures, and chemical pesticides supplemented with biopesticide are effective to increase yield as well as quality of the onion bulb.The improvement in bulb diameter, size index and yield attributes due to phosphate solubilizers may be due to the ability of Ps. fluorescens to solubilize and increase availability from insoluble or fixed phosphorus to soluble or readily available phosphorus (P).Similar findings have been reported by other workers (Gupta, 2009;Verma and Mathur, 1989).
The favorable nutritional environment in the root zone created by the addition of organic manures and biofertilizers resulted in increased absorption of the nutrients from soil which was responsible for increasing the yield of onion bulbs ( Gupta et al., 2009).Similar findings have been reported in carrot (Luzzati et al., 1980) and in potato (Mandal and Roy, 2001).The higher yield was obtained in potato based cropping systems by the use of fertilizers in combination with organic manures than the use of inorganic fertilizers alone (Sharma and Dua, 1995).Studies conducted on integrated nutrient management (INM) in onion bulb crop improved the quality and yield of onion bulbs through integration of chemical fertilizers along with organic manures (Singh et al., 2001).

Figure 3 :
Figure 3: Percent disease control (PDC) of stemphylium blight in different treatments over control CD (P=0.05)13.82 under field condition