Yellow Vein Mosaic disease in kenaf ( Hibiscus cannabinus l . ) under different sowing dates in two agroecologies

Determination of appropriate sowing dates is an important approach towards obtaining optimum crop yield as it affects the resistance/susceptibility of crops to insect pests and diseases. The study investigated the effect of three sowing dates (May, June and July) on the occurrence and incidence of yellow vein mosaic disease in kenaf variety (IFEKEN-100) planted in the experimental fields of the Institute of Agricultural Research and Training (IAR&T) located in Ibadan and Ilora. The incidence of yellow vein mosaic disease was high in May at the two locations with means of 25 and 30% for Ibadan and Ilora, respectively. Plant height was not significantly different in the two locations across the three months. The highest stem diameter was obtained in May from Ilora and Ibadan with means of 1.44 and 1.53 cm, respectively. The best bast fiber yield was recorded in June at Ibadan with a mean value of 1.72 tha-1. Nucleic acid spot hybridization (NASH) was used to confirm the disease and the results revealed that Begomovirus was present in kenaf sowm in the two locations during the period of the three months except in kenaf sown in July at Ilora. The results of this study revealed the importance of sowing dates on the occurrence of viral diseases on the field. If the sowing date is optimum, the effect of viruses may not be pronounced in the crop as seen in the month of June having relatively low virus incidence as well as the highest plant height and bast fibre yield.

vegetable and fibre crops in tropical and subtropical At 6 weeks after sowing, plant height was determined countries (Khan, 2000;Boulton, 2003).The genus by using a meter rule to measure the shoot of the plant Begomovirus contains more than 200 species from the base to the apex in cm.Stem diameter was (Fauquet et al., 2008) and belongs to the taxonomic determined by measuring the diameter of the stem in family Geminiviridae.Begomoviruses are cm using a venier caliper.The bast fibre was determined characterised by having circular single-stranded by weighing the fibre obtained from the tagged plants -1 DNA genomes encapsidated within twinned after retting and was later extrapolated to tha .isometric particles (Lazarowitz 1992;Briddon and Markham 1994)

and are characteristically
Nucleic acid extraction transmitted by whiteflies (Bemisia tabaci).It causes Symptomatic leaves showing yellow vein yellowing of veins and veinlets followed by mosaic pattern were collected from kenaf plants at six complete chlorosis of the leaves of the affected weeks after planting from the two locations.Where plants (Chatterjee et al., 2005a).yellow vein mosaic disease was not observed, Studies on the viral diseases especially asymptomatic leaf samples were collected.The leaf yellow vein mosaic disease of kenaf have been samples were dried over Calcium chloride until when reported by different authors from different needed.Nucleic acid extraction kit obtained from Agdia countries (Chatterjee et al. 2005b;Ghosh et al., Inc., Elkhart, Indiana, USA was used to extract nucleic 2007) but there is a dearth of reports on kenaf acids from the leaf samples using the protocol of viruses in Nigeria.This study was, therefore, carried Podleckis et al. (1993).out to investigate the presence and incidence of One gram of the dried leaf samples was ground yellow vein mosaic disease in kenaf under different in 1 g of distilled water using mortar and pestle.planting dates in two agro-ecologies.It is also Approximately 50 µl of the plant sap was transferred important to determine the influence of the virus into an eppendorff tube containing 450 µl of AG1 Lysis and planting dates on the growth and yield of kenaf Buffer.The tubes were vortexed for 2 mins and fibre.
incubated at room temperature for 5 mins.Then the tubes were centrifuged at a maximum speed of 12000 x Materials and Methods g for 3 mins.About 300 µl of the supernatant was transferred into a new centrifuge tube containing 350 µl Experimental materials and design of 100% ethanol.The mixture was vortexed for 2 mins Kenaf variety IFEKEN 100 collected from and it was centrifuged (Eppendorf microcentrifuge, the Germplasm unit of Kenaf and Jute Improvement 14,200 rpm) at maximum speed for 5 mins.Programme, Institute of Agricultural Research and The supernatant was carefully decanted and Training (IAR&T), Ibadan was used in this study.
the pellet was washed twice in 300 µl of 70% The experiment was conducted at the Research 0 0 isopropanol.The tubes were inverted on a paper towel farms of IAR&T, Ibadan station (7 38'N, 3 84'E 182 0 0 and allowed to dry at room temperature for 10 mins.masl) and Ilora station (7 81'N, 3 82'E 278 masl) in Pellets were later resuspended in 25 µl of nuclease-free 2016.
water.The experimental area was laid out in a randomized complete block design with three Nucleic acid hybridization assay replicates.The blocks were divided into three plots measuring 3 x 3 m each, representing three Approximately 3.0 µl of the extracted nucleic planting periods: May, June and July.The plant acids were loaded onto a nylon membrane supplied by spacing was 50 x 20 cm and the number of Agdia's laboratory, USA.The membrane was introduced plants/hill was three and later thinned to one to labeled probes of Begomovirus in Agdia's laboratory plant/hill giving a total plant population of 277 000 where hybridization of complementary nucleic acid -1 plants ha .fragment occurred.Chemiluminescent detection was In each month at 6 weeks after sowing, used to produce a visual spot by exposing the disease incidence was determined by observing membrane to film, indicating a positive result.Negative leaves showing the symptoms of yellow vein mosaic result did not produce spot on the membrane.disease such as yellow veins and veinlets, mosaic and chlorosis.The symptomatic leaves were

Statistical analysis counted and expressed as percentage of the total
The data obtained were analyzed with the Statistical number of plants sampled (Kareem et al., 2016).
Package for Social Sciencies (SPSS) version 16.The Disease Incidence (%) = (Number of data were subjected to symptomatic plants/ Total number of plants) x 100 analysis of variance and means were separated with Five pre-tagged plants were randomly selected for Duncan's multiple range test at P < 0.05. the determination of some agronomic parameters.

Results
1).Similarly, In Ilora, the incidence was high when it was sown in May (30%), this was followed by kenaf Incidence of Yellow vein mosaic disease in kenaf sown in June (22.7%).However, a very low incidence Incidence of Yellow vein mosaic disease at was recorded in July with a value of 2% (Fig. 1).Ibadan was high in kenaf sown in May (25%) compared to June (12.3%)and July (16.5%) (Fig.

Fig. 1. Incidence of Yellow vein mosaic disease in kenaf
Table 1.Effect of planting dates on growth and yield characters of kenaf This was followed by sowing in June at Ibadan station Growth and yield characters (1.25 cm) (Table 1).Plant height at Ibadan was not significantly The fibre yield of kenaf at Ibadan was better different at P < 0.05.withmean values ranging from than that of Ilora.The highest bast fibre yield of 1.7 tha-95.4 to 102.7 cm.Similarly, plant height at Ilora was 1 was obtained from Ibadan when the kenaf variety was not significantly different with the mean values sown in June while the lowest bast fibre yield of 0.26 ranging from 57.9 and 93.8 cm.The stem diameter -1 tha was obtained when the variety was sown in June at of the May planting date at Ibadan and Ilora were Ilora (Table 1).significantly higher than the other months with mean values of 1.53 and 1.44 cm, respectively.May to July were positive to the complementary probe Nucleic acid spot hybridization assay (NASH) used in the hybridization assay.At Ilora, positive results T h e N A S H a s s a y r e v e a l e d t h a t for presence of Begomovirus were revealed for May and Begomovirus was present in infected/symptomatic June planting and a negative result for July planting leaves of kenaf with yellow vein mosaic pattern (Fig. (Table 2).2).All the leaf samples collected at Ibadan from Means followed by the same letter along the column are not significantly different according to Duncan Multiple range test at P ≒ 0.05.factors such as environment and climatic conditions can Narula et al. (1999) recorded high incidence of affect crop yield.Sowing date as a factor affecting both cotton leaf curl disease during the rainy season.
plant growth and yield depends on the prevailing Also, the conducive environmental factors which environmental conditions especially temperature and facilitate the build up of whitefly populations during relative humidity (Elhag and Ahmed, 2014).the early crop growth period could be responsible The result obtained from the NASH study for the high incidence (Roy et al., 2009).The very revealed the presence of Yellow vein mosaic disease on low incidence in kenaf sown in July at Ilora could be the kenaf fields.The presence of the virus on kenaf attributed to the fact that the taller plants from the fields is impossible because kenaf belongs to the kenaf sown in the previous months i.e.May and Malvacea family which is known to be infected by June prevented the landing of the Begomovirus Begomoviruses.Ghosh et al. (2007) reported the vector on the shorter plants.Another reason is that occurrence, distribution and disease incidence of Yellow the population of the vector could have reduced as vein mosaic disease of kenaf in both commercial and a result of the delay in planting date.Alegbejo experimental farms in India using southern (1999) reported in his work that there was hybridization with Begomovirus specific probe.reduction in the average number of virus-vectoring The kenaf variety used in this study showed beetles caught per plot as a result of delay in sowing susceptibility to Yellow vein mosaic disease as shown by date.
the NASH test except for the month of July at Ilora which Results on plant height and stem diameter gave a negative result.The positive results could be due showed that early sowing of kenaf apparently led to to the fact that the population of insect vectors (Bemicia better growth parameters when compared with late tabaci in this case) which transmit viruses is usually high sowing.Ossom and Kunene (2011) reported poor during raining season while the negative result could be seed emergence and short okra plants as a result of attributed to the usual low incidence of the vector, late sowing compared to early sowing.In Ibadan, Bemicia tabaci responsible for the transmission of the kenaf sowed in June produced the best bast Yellow vein mosaic viruses in the month of July.Mastoi fiber yield while the yield of Ilora was very low in the et al. ( 2013) reported that the peak infestation of same month.This can be explained by the fact that whitefly in okra varieties was observed in June and pest kenaf sowed in June at Ibadan station had the population started declining on subsequent

Fig. 2 .
Fig. 2. Nucleic acid spot hybridization (NASH) test of extracted DNA from kenaf leaves showing yellow vein mosaic disease at 6 weeks after sowing. 1 = positive control.

Kareem et. al./ Nig. J. Biotech. 33 (2017) 83-88 Discussion highest
plant height of 102.7 cm which could have High incidence of Yellow vein mosaic virus contributed to the high yield.Elhag and Ahmed (2014) was observed in kenaf sown in May at Ibadan and have reported that good vegetative growth and pod Ilora; this could be as a result of lush growth of yield means high seed yield.Apart from this, other weeds and whiteflies during the rainy season.

Table 2 .
Occurrence of yellow vein mosaic disease in kenaf using nucleic acid spot hybridization assay + = Begomovirus present, -= Begomovirus absent Kareem et.

al./ Biotech. 33 (2017) 83-88
Conclusion Elhag, A. Z. and Ahmed, A. W. (2014).Effect of cultivar Sowing date is a very important factor that and sowing date on okra (Abelmoschus esculentus L. determines the resistance/susceptibility of crops to Moench.) seed yield.Univ.J. of Appl.Sci.2(3): 64-67.pests and diseases which directly or indirectly DOI: 10.13189/ujas.2014.020302affects the agronomic and yield characters of crops.Selection of appropriate sowing date in a particular FAO (1998).FAO production year book Vol 3. year goes a long way in optimizing crop yield.This date should not be fixed over years as a result of FAO (2003).Consultation on Natural Fibers, The changing climatic conditions experienced year in production and consumption of kenaf in China.ESCyear out.Therefore, the determination of the Fibers Consultation NO: 03/6.sowing dates of crops should be a continuous for yield optimization.Therefore, this study Farrag, M. M. (1995).Yield of 23 mung bean accessions concludes that June is the most appropriate sowing as affected by planting date under El-Menia conditions.date of kenaf.Assiut J. Agric.Sci.26(2): 49-62.