Incidence and Severity of Virus Diseases of Okra (Abelmoschus Esculentus l Moench.) Under different Mulching Types

Okra (Abelmoschus esculentus L Moench) is of the family Malvaceae. There are four known domesticated species of Abelmoschus. Among these, A. esculentus (common okra) is most widely cultivated in South and East Asia, Africa, and the southern USA. In the humid zone of West Africa Countries, A. caillei (West African okra) with a longer production cycle, is also cultivated [1]. Plants of A. manihot sometimes fail to flower and this species is extensively cultivated for leaves in Papua New Guinea (Farooq 2010), Solomon Islands and other South Pacific Islands [2]. As a plant originated in Africa, okra is now cultivated in tropical, subtropical and warm temperate regions around the world [1]. The economic importance of okra cannot be overemphasized. However, it is widely cultivated fruit vegetable and fruit crop by subsistence farmers of guinea and Sudan savannah of West Africa (Kumar 2010).

be pulverized, moistened and enriched with organic matter before sowing. Also, it is ideally recommended to plant okra on plains of sandy loam soil of pH of 6.0 to 6.8 for an excellent production especially when incorporated with organic mulch well treated [5].
Okra cultivation and production has been widely practiced because of its importance to the economy development and can be found in almost every market in Africa (AVRDC, 2004). Okra is the most important fruit vegetable crop and a source of calorie (4550Kcal/kg) for human consumption. It ranks first before other vegetable crops [6]. Okra contains carbohydrate, protein and vitamin C in large quantities [7]. The essential and non-essential amino acids that okra contains are comparable to that of Soybean.
It was also reported by Eke et al. [8] that fresh okra fruit is a good source of vitamins, minerals and plant proteins. As a result it plays a vital role in human diet; it can be consumed boiled, fried or cooked for the young immature fruits. The word mulch has been probably derived from the German word "molsch" means soft to decay, which apparently referred to the use of straw and leaves by gardeners as a spread over the ground as mulch [9].
Mulches are used for various reasons in agriculture but water conservation and erosion control are the most important objectives particularly in arid and semi-arid regions. Other reasons for use of mulching include soil temperature modification, weed control, soil conservation and after decomposition of organic mulch add plant nutrients, improvement in soil structure, increase crop quality and yield. Mulching reduces the deterioration of soil by way of preventing the runoff and soil loss, minimizes the weed infestation and reduces water evaporation [9]. Thus, it facilitates more retention of soil moisture and helps in control of temperature fluctuations, improves physical, chemical and biological properties of soil, as it adds nutrients to the soil and ultimately enhances the growth and yield of crops [10]. In addition mulch can effectively minimize water vapour loss, soil erosion, weed problems and nutrient loss [11]. Organic mulches are efficient in reduction of nitrates leaching, improve soil physical properties, prevent erosion, supply organic matter, regulate temperature and water retention, improve nitrogen balance, take part in nutrient cycle as well as increase the biological activity [12]. Natural materials cannot be easily spread on growing crops and require considerable human labour [13]. Chen and Katan [14] also reported high water content in the top 5 cm of soil (an increase of 4.7 per cent in clayey, 3.1 per cent in loamy and 0.8-1.8 per cent in sandy soil) with polythene mulch. Das, et al., 2000 observed that use of polyethylene mulch in the field, increased the soil temperature especially in early spring, reduced weed problems, increased moisture conservation, reduction in certain insect pest population, higher crop yield and more efficient use of soil nutrients.
Abu-Awwad (2009) showed that covering of soil surface reduced the amount of irrigation water required by the pepper and the onion crop by about 14 to 29 and 70 per cent respectively. Trials conducted in the higher potential areas of Zimbabwe indicated that mulching significantly reduced surface runoff and infiltration [15].
Therefore, the main objectives of this paper are to investigate the use of mulching as a cultural practise in ameliorating viral diseases incidence and severity on Okra; to evaluate the effect of treatment combinations {mulching materials (dry grasses and polythene film).

Material and Methods
The experiment was conducted at the Teaching and Research June to October and with a brief dry spell, which in most cases occur in the second half of August. The peak rainfall period is June/ July and September/October, while the short dry season last from November to December. Also, the daily temperature ranges from 26 o C and 49 o C [16]. The place of the field Experiment falls under AEZ-(Agro Ecological zone). The topography of the land was medium high with sandy loam soil. And this area has been proven to be suitable for okra cultivation [17].

The experiment was laid down in 3 X 4 Factorial Design fitted
into Randomized Completely Block Design (RCBD) with three (3) replicates. Each block consists of 12 treatment combinations. Total land area planted measured 30m X 15m, Block sizes measured 5 X 15m with 1m alley ways between replicates. Experimental field was partitioned into three blocks with mulching types within the plots. Each experimental plot consisted of 24 ridges each 5m long. The Mulching types were at 3 levels namely: No mulching, plastic (polythene) mulching, organic mulching (dry grass). Each treatment was replicated 3 times and was randomly assigned to each plot.
All data were collected on a weekly basis on growths, yield and disease parameters as at when due in the morning and the

Results
Analysis of the results on mulching types showed that at 3rd and 4th week after planting, highest incidence were recorded on mulching level of no mulch (13.21% and 23.7%) respectively while mulching types of polythene had the lowest % incidence (3.29% and 5.66%) respectively. However, it implied that the mulching type level of no mulch and grasses are not significantly different when compare with each other. However, they are significantly different to polythene mulching type. At week 5, there was significant difference between regimes where dry grasses mulching was applied and that polythene mulching types while there was no significant difference between the regime where no mulching was applied and the dry grasses mulching type's regimes.
The values from week 6 and 7 follow the same trend where at week 6 and 7, there was significant difference between the regimes without mulching types and the polythene mulching types regimes while there was no significant difference between regimes where mulching was not applied and dry grasses mulching type ( Table 1).
The main effect of the mulching types in Table 2 showed that at 3 rd week after planting no mulch had the highest percentage severity of 17.72% followed by dry grasses (16.57%) and polythene (5.36%) had the lowest severity. However, it implied that there was no significant difference between mulching type level of no mulch and dry grasses while polythene mulch is significant different from no mulch and dry grasses.        (Table 6).

Discussion
Farmers are continually developing a stronger interest in okra production given its potential as an economic crop and its ability to grow optimally in the absence of fertilizers and also its ability However, the effect of mulching treatment combinations tried in this study had effects on the incidence and severity of viral diseases.
This study showed that the incidence of virus diseases was lowest at the treatment combination where polythene mulching was applied and the highest at the no mulch. Therefore, it implied that low virus incidence existed under the polythene mulch. This assertion is in agreement with Alegbejo [18] when they reported that viral incidence decreases progressively with weeding regime.
This development must have been a result of polythene inhabiting the growth of weeds that usually serve as abode of potential vectors of the viruses [19]. Viral incidence was observed to be the highest at the regime that was not weeded and lowest at the regime that was weeded thrice. The reason for high incidence recorded was attributed to high weed interference. This declaration is in conformity with Hooks et al. (2012) who reported that weeds acts as reservoirs for insect, disease agent and nematodes.
This study also showed that interactive effective of mulching could effectively reduce incidence of virus diseases but it is better determined by polythene mulching type and this was in accordance with report of Holland, [20] who reported that polythene mulched rhyzosphere had greatest potential that aid growth and development of herbaceous plant combating viral diseases. Also, yield reduction due to insect pest was estimated to be 89.7-91.6% in regime with dry grasses compared to no mulch and polythene mulch, this assertion is in agreement with Aiyelaagbe and Jolaoso [21] who reported that damage by insect pest on okra can be as high as 80-100% if not effectively controlled. In this study, it was showed that Okra mosaic virus was the most virulent virus that was positive irrespective of control measures applied this was so because OkMV had the widest host range [18].
According to Alegbejo, OkMV's epidemiology premised on early rains with intermittent dry and wet spell also other conditions that favour OkMV are warm weather condition and availability of abundant vectors and alternative host. More so, the study also showed that a treatment combination of polythene mulching and weeding thrice produced highest yield parameters. This suggests that weeding could be effective in viral disease control, it is better determined on polythene mulch. This could be explained by protection provided by polythene against insect that harboured in alternative host (weed) that surrounded the okra plant and this corroborates data obtained by Bhardwaj [13,[22][23].