Introduction according to the cultivars [9]. OYDV may reduce the seed production of onion seed crops by up to 50%.

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:

salanagar@hotmail.com.

measures.

Effect of Natural Infection with Onion Yellow Dwarf Virus (OYDV)

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 relation to plant yield, plants grown in the field were

plants. The infection resulted in 27.42% reduction in 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).

Weight of bulb (g) Rep. Healthy Infected Healthy Infected Healthy Infected Healthy

Pseudostem length (cm)

No. of leaves/plant

Weight of plant (g)

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

0.0 27.42 0.0 29.14 0.0 31.9 0.0 41.8 * Total of 20 replicate plants.

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.

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