Effect of Natural Infection with Onion Yellow Dwarf Virus (OYDV) on Yield of Onion and Garlic Crops in Egypt

Journal of Life Sciences 5 (2011) 634-638 Effect of Natural Infection with Onion Yellow Dwarf Virus (OYDV) on Yield of Onion and Garlic Crops in Egypt Salah Elnagar, Mohamed Abdel-Kader El-Sheikh and Abeer Salah El-Deen Abd El-Wahab Department of Economic Entomology and Pesticides, Faculty of Agriculture, Cairo University, Cairo 12613, Egypt Received: December 10, 2010 / Accepted: February 17, 2011 / Published: August 30, 2011. Abstract: Present work highlights, first time in Egypt, the impact of OYDV infection on crops production. Plants grown in the field were individually labelled as either apparently healthy or diseased and were marked for harvesting. The percentage of yield loss due to viral infection was determined, on the basis of the average yield parameters of the healthy plant. The natural infection with OYDV in onion and garlic fields resulted in a substantial reduction in pseudo-stem length, number of leaves, plant weight and weight of bulb as well as number and weight of cloves. Results clearly indicate the impact of natural infection with OYDV on the crop yield of infected onion and garlic plants in comparison with the virus-free (uninfected) ones. The largest reduction in the yield of infected plants occurred in Chinese garlic (Seds40) followed by (Baladi) garlic and onion Giza 20. This information suggests that measures have to be taken to prevent natural infection with OYDV into and within onion and garlic fields in order to avoid yield loss. Key words: Onion yellow dwarf virus (OYDV), yield reduction, onion, garlic. 1. Introduction according to the cultivars [9]. OYDV may reduce the seed production of onion seed crops by up to 50%. Both onion and garlic are important field crops OYDV caused significant decline in seed yield, cultivated in many areas in Egypt. The bulbs have to be however seed vitality was not affected [10]. The stored to meet the increase demand in both local amount of damage caused by OYDV disease varied consumption and export. depending on the plant age at the time of infection [11]. Onion yellow dwarf potyvirus (OYDV) was first Bulbs from diseased plants kept poorly in storage [12]. described [1, 2] in Egypt [3], yet its impact was not Present work highlights, first time in Egypt, the impact reported. The virus causes striping, curling and of OYDV infection on the crop production. distortion of flower stems, reduction in the number of flowers and seeds, and impairment of seed quality [4]. 2. Material and Methods OYDV was isolated and identified from onion leaves Field survey on Alliaceae plants took place in Giza showing mosaic and yellow streak [5, 6]. OYDV was Governorate during two successive growing seasons found in 40% of the garlic using DAS-ELISA [7]. Up (2000/2002). The Alliaceae crop species and cultivars to 45% yield loss due to GMV (Garlic mosaic virus) were onion, Allium cepa L. “Giza20” and Baladi garlic, infection reported [8]. Bulbs harvested from Allium sativum L. and Chinese garlic, Allium sativum L. mosaic-affected plants were much smaller in size and “Seds40”. These crops were sown at the end of cloves. Potential yield loss of garlic (Allium sativum) September for the two growing seasons, in an area of due to OYDV-infection, ranged from 39% to 60% about 1/3 Feddan (one Feddan = 4200 square meter). The experimental area received all the usual Corresponding author: Salah Elnagar, professor, research agricultural practices except for any pest control field: economic entomology and pesticides. E-mail: [email protected]. measures. Effect of Natural Infection with Onion Yellow Dwarf Virus (OYDV) 635 on Yield of Onion and Garlic Crops in Egypt Regular observations were made for the appearance 3. Results of any disease syndromes due to virus infection. Plants The effects of natural infection with OYDV on showing signs of leaf stripping, stunting, dwarfing, onion and garlic yields were studied. yellowing, mosaic and crinkled leaves were labelled The natural infection with OYDV greatly reduced and weekly observed. Leaf samples and whole plants the average yield per plant for both onion and garlic. were taken to the laboratory for both sap (mechanical) Onion yield: The obtained data of natural infection and aphid inoculation tests as well as the ELISA test to with OYDV in Table 1 indicate a remarkable reduction confirm the causative disease agent [13]. in all tested yield parameters compared to the healthy To monitor the development of virus infection in plants. The infection resulted in 27.42% reduction in relation to plant yield, plants grown in the field were individually labelled as either apparently healthy or the length of onion plant. Fig. 1 shows stunting of diseased. Each plant represented a replicate of either infected plants and Table 1 demonstrates a reduction of the infected or the healthy group and was marked for 29.14% in the number of onion leaves due to virus harvesting. All plant-replicates were measured for infection in comparison with healthy plants. The height (cm), number of leaves/ plant, no of bulbs or estimated average number of 8.75 leaves/healthy plant cloves/plant, weight of bulbs or cloves/plant (g), and was reduced to 6.2 leaves/infected plant. weight of seeds/plant (g). The percentage of yield loss Table 1 and Fig. 1 clearly confirm the effect of due to viral infection was determined, on the basis of OYDV on the plant weight (31.9% reduction). The the average yield of the healthy plant, using the estimated average weight of healthy plant was 118.1 g following formula [14]: compared to 80.36 g of naturally infected onion plant. YL (%) = (YH-YD)/YH × 100 The average weight of infected bulb (62.61 g/bulb) was Where YL = Yield loss; YH = Yield of healthy plant; highly reduced (41.8% reduction), as compared to YD = Yield of diseased plant. 107.5 g of a healthy bulb (Fig. 1 and Fig. 2). Table 1 Recorded reductions in different yield parameters of onion plant (Giza20) due to natural infection with OYDV (Giza, 2001/2002). Pseudostem length (cm) No. of leaves/plant Weight of plant (g) Weight of bulb (g) Rep. Healthy Infected Healthy Infected Healthy Infected Healthy Infected Total* 361 262 175 123 2362 1607.2 2150.5 1252.2 Average 18.05 13.1 8.75 6.2 118.1 80.36 107.5 62.61 Actual yield 100 72.57 100 70.85 100 68.1 100 58.2 % Reduction 0.0 27.42 0.0 29.14 0.0 31.9 0.0 41.8 * Total of 20 replicate plants. 45 41.8 % Reduction 40 35 31.9 29.14 30 27.42 25 20 % Reduction 15 10 5 0 Pseudostem length (cm) No. of leaves/plant Weight of plant (g) Weight of bulb (g) Parameters Fig. 1 Reduction in different yield parameters due to natural infection with OYDV in onion Giza 20. 636 Effect of Natural Infection with Onion Yellow Dwarf Virus (OYDV) on Yield of Onion and Garlic Crops in Egypt cloves/bulb in the healthy plant. The reduction percentage in the number of cloves in Chinese garlic was 47.37% while it was 20.2% in Baladi garlic (Fig. 3). Correspondingly, the weight of bulbs was reduced by 71.92% and 44.9% in Chinese garlic and Baladi garlic, respectively. In general, the largest reduction in the yield of Fig. 2 Onion Giza 20 yield in the field (Giza, 2001/2002). I = infected plants occurred in Chinese garlic (Seds40) infected plant with OYDV. H = healthy plant. followed by (Baladi) garlic and onion Giza 20. Garlic yield: The average reduction in the 4. Discussion pseudo-stem length of naturally infected garlic plants Chinese garlic (Seds40) was as great as 47.6% and was The presence of the aphid-borne OYDV in Egypt is 16.76% in Baladi garlic. The reduction was 27.75% partially characterized from naturally infected onion and 20.11% respectively in the number of leaves of and garlic plants [3] and symptoms similar to those infected plants (Table 2 and Fig. 3). described in the present study. In addition, the virus Table 3 and Fig. 3 show that the infection resulted in was confirmed by ELIZA tests. The reduction in onion an average reduction in Chinese garlic plant weight of and garlic yield due to the infection with OYDV is about 56.24% (Figs. 4 and 5) and 47.12% in Baladi estimated by reduction in plant length, number of garlic (Figs. 6 and 7). The weight of Chinese garlic leaves, weight of plant and weight of bulbs and no. of (Seds40) bulb was reduced by 58.78% due to infection. cloves in garlic. The highest percentage of reduction In the case of (Baladi) garlic, the reduction in bulb occurred in Chinese garlic “Seds40” cultivar and weight was 46.56% (Table 3, Fig. 3). The average “Baladi” garlic came second followed by onion. number of cloves of infected Chinese garlic plant Similar results elsewhere [8, 15] reported 45% yield (Seds40) was 8 cloves/bulb, compared to 15.5 loss due to mosaic virus infection. In the present study, Table 2 Reductions in the different yield parameters of Chinese garlic A. satirum (Seds40) due to natural infection with OYDV (Giza, 2001/2002). Pseudstem length No. of leaves Weight of plant Weight of bulb No. of cloves/bulb Weight of cloves (cm) (g) (g) (g) Healthy Infected Healthy Infected Healthy Infected Healthy Infected Healthy Infected Healthy Infected Total* yield 722 378.4 22.7 164 798 349.2 751.75 309.95 304 160 726.5 210 Average yield 36.1 18.92 11.35 8.2 39.9 17.46 37.58 15.49 15.2 8.0 36.325 10.2 Actual yield 100 52.40 100 75.24 100 43.75 100 41.2 100 52.63 100 28.07 % Reduction 0.0 47.60 0.0 27.75 0.0 56.24 0.0 58.78 0.0 47.37 0.0 71.92 * Total of 20 replicate plants.

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