Mohamad Alkhalaf
General Commission for Scientific Agricultural Research-
Aleppo Research Center
Aleppo University, Faculty of Agriculture
2009

Abstract

This experiment was carried out to assess the effectiveness of using a sprayer with compressed air to mechanically inoculate Bean yellow mosaic virus as a replacement for manual inoculation in screening for virus resistance during 2005/2006 growing season.
Experimental plots (2.7 m2) were planted with faba bean cv. Syrian Local (ILB 1814), and mechanically inoculated with BYMV (Isolate SV205-85).
The inoculums were prepared by grinding infected plant leaves using 0.01M potassium phosphate Buffer (KPO4), pH= 7.2, or water (dH2O), with or without Celite, and four BYMV dilutions were used. Results showed no significant difference (P =0.05) in the infection rate when using potassium phosphate buffer or water, whereas there was significant difference (P =0.05) in infection rate when Celite was added, and no significant difference (P =0.05) in the infection rate among the different dilutions used.
The highest rate of BYMV infection achieved was 81%, when the inoculum was diluted 1:20 in potassium phosphate buffer in the presence of Celite.
A field survey to determine the extent of Bean yellow mosaic virus (BYMV, genus Potyvirus, family Potyviridae) spread in cool-season food legumes and weeds in four main areas in Syria (coastal, northern, southern and central) was conducted during three growing seasons (2004/2005, 2005/2006 and 2006/2007).
The survey covered 235 fields, a total of 3750 samples with symptoms suggestive of virus infection, 10785 random samples, and 428 weed samples were collected and tested by tissue-blot immunoassay (TBIA).
Results showed that BYMV was detected in all surveyed areas with the highest incidence in faba bean in the coastal zone, followed by chickpea, lentil and pea with different infection rates.
The virus was also detected for the first time on three weeds, Melilotus sp., Rhaphanus raphanistrum L., and Molucella sp.
A total of 514 faba bean, 123 lentil, and 53 pea genotypes from the Gene Bank of ICARDA, originating from five continents and ICARDA breeding program, were evaluated during the 2004/2005, 2005/2006 and 2006/2007 growing seasons, for their reaction to a Syrian isolate of bean yellow mosaic virus (BYMV, genus Potyvirus, family Potyviridae).
All plants were inoculated mechanically at the 4-leaf stage under field conditions, and one replicate was kept as healthy control.
Results showed that most of the genotypes were infected, and the range of virus infection was 0-100%. Yield loss ranged between 0 – 100%.
The harvested seeds from the screening experiments were used to study the variability in BYMV seed-transmission rate.
All seeds were planted in trays with sand, and germinated seedlings were tested for the presence of BYMV using TBIA.
Results revealed that BYMV was transmitted in faba bean and lentil seeds, and not in pea seeds.
In addition, infection with BYMV affected the color and shape of the seeds, which reduced their market value, especially when used for canning.
The movement and multiplication of bean yellow mosaic virus, (BYMV, genus Potyvirus, family Potyviridae) was evaluated in 12 faba bean, 13 lentil, and 15 pea genotypes which varied in sensitivity and susceptibility to virus infection. Experiments were conducted under artificial infection conditions in a glasshouse during 2007.
All plants were inoculated at the four leaves stage. Five plants from each genotype were tested for 24 days after inoculation at two days interval.
Different plant parts (growing point, stem, stem base, root) were cut and printed on nitrocellulose membrane (NCM), and then all the membranes were tested at the same time by the tissue blot immuno-assay (TBIA) at the end of the experiment.
Virus concentration in each section was estimated by using a 0-3 scale and accordingly relative TBIA values were estimated for the different faba bean genotypes, and a 0-1 scale for lentil and pea genotypes.
The TBIA results revealed that the systemic movement and multiplication of BYMV were slower in resistant than in susceptible genotypes.
Eight to ten days after inoculation, the virus was detected in all four plant parts of sensitive faba bean (ILB 6101, ILB 6167, ILB 2134, ILB 3038, ILB 454, and PBL 507), pea (IFPI 378, IFPI 953, IG 134573) and lentil (ILL 262, ILL 1645, ILL 4400, and ILL 8635) genotypes tested. Whereas, the virus was not detected in resistant pea (IFPI 224, IFPI 791, IFPI 1643, IFPI 2527, IFPI 3378, IFPI 3660, IG 134697), and resistant lentil (ILL 8216, ILL 7163, ILL 4736, ILL 336, ILL 83) genotypes until 24 days after inoculation.
These findings suggest that BYMV movement and multiplication can be useful criteria in differentiating between resistant and susceptible faba bean, lentil and pea genotypes at around 8-10 days after inoculation.
An experiment was conducted to study the effect of applying four sprays of Thiamithoxam (insecticide) or summer mineral oil on the rate of virus spread under field conditions during the 2005/2006 growing season.
Results showed significant difference (P =0.05) in virus spread between treatments and control.
Thiamithoxam treatment was significantly better than mineral oil and led to 18.4% increase in yield.
A study was carried out to evaluate the effect of bean yellow mosaic virus infection on the yield of faba bean cv. Syrian Local (ILB 1814) during the 2006/2007 and 2005/2006 growing seasons under field conditions and mechanical inoculation with different infection rates 0-100% and dates of inoculation.
The results obtained indicated that virus incidence and date of inoculation adversely affected faba bean yield. Results also showed that date of inoculation and infection rate had a significant (P =0.05) effect on yield.
Yield regression line showed that yield has direct relationship with inoculation delay and inversely proportional with infection rate.<br>Bean yellow mosaic virus (BYMV, genus Potyvirus, family Potyviridae) was studied by comparing sequences from the coat protein (CP) gene of a Syrian isolate with sequences of six other isolates from NCBI database. A homology tree of the CP sequences was developed using the DNAMAN Software. BYMV isolates were grouped in two separate clusters, the first included the Syrian isolate together with Indian, Australian and Japanese isolates, whereas, the second included BYMV isolates from China, Netherlands and USA. Moreover, the homology tree showed that the Syrian isolate was very close to the Indian one with 99% homology.
The possibility of using both sides of the nitrocellulose membrane (NCM) by tissue blot immunoassay (TBIA) for the detection of Bean yellow mosaic virus (BYMV, genus Potyvirus, family Potyviridae) was investigated.
Faba bean, lentil and pea plants infected with BYMV were printed on (i) one side of NCM, (ii) on both sides of NCM, and (iii) on the other side of a processed and/or unprocessed NCM already printed with plant tissues on one side.
The results showed that BYMV can be easily detected in faba bean, lentil and pea plants by TBIA using both sides of the membrane.
The use of both sides of the NCM reduced the cost of testing by 50%. The results also showed that the virus can not be transmitted mechanically from the printed infected blots on NCM to a healthy plant, and consequently, it does not permit the movement of virus from one location to another distant location.