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Screening of Maize Storage varieties resistant to corn weevil

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  • Save International Journal of Plant Research 2013, 3(3): 17-22 DOI: 10.5923/j.plant.20130303.01 Screening of Stored Maize (Zea mays L.) Varieties Grain for Tolerance Against Maize Weevil, Sitophilus zeamais (Motsch.) Simbarashe Muzemu1,*, James Chitamba2, Sipiwe Goto1 1Department of Horticulture, Faculty of Natural Resources M anagement and A griculture, M idlands State University, P. Bag 9055, Gweru, Zimbabwe 2Department of Agronomy, Faculty of Natural Resources M anagement and A griculture, M idlands State University, P. Bag 9055, Gweru, Zimbabwe Abstract Insect pests cause major damage to stored maize grain thereby reducing its weight, quality and germination vigour. Five open pollinated maize varieties (ZM401, ZM309, ZM 521, ZM 421 and Hickory King) and one hybrid maize variety (SC709) were evaluated for tolerance and their effects on progeny development against the maize weevil, Sitophilus zeamais (Motsch.). The experiment was laid in a rando mised complete block design, with 6 treat ments replicated 5 times. 100g maize grain was infested with 100 three week old unsexed pure culture adult weevils in 750 ml jars. After 14 days oviposition period, adult weevils were sieved out and parent weevil mo rtality determined. After a fu rther 45 days, number of weevils emerged, percentage grain weight loss and number of damaged kernels were determined. Percentage kernel germination was determined through a germination test after 45 days of weev il attack. There were significant differences (p<0.05) in nu mber of parent weev il mortality, nu mber of weev ils emerged, grain weight loss, kernel damaged and germination percentage a mong varieties. ZM 421 and ZM 521 variet ies showed potential to S. zeamais progeny suppression and tolerance as evidenced by high parent weevil mortality, low weevil e me rgence, less grain weight loss, low grain da mage and high germination percentage. Keywords Stored Maize Grain, Sitophilus Zeamais, Maize Varieties, Progeny Suppression 1. Introduction Maize (Zea ma ys L.) is the most important crop in Zimbabwe and Southern Africa since it is a staple food crop which is widely grown by most smallholder farmers who significant ly contribute to nat ional production [1,2]. The necessity to increase maize product ion cannot be over emphasized; in Zimbab we it ranks first in terms of total cereal production, number of producers and area grown[3]. It has been reported that the crop accounts for 70% of the total of the total hectarage under cereals with 60% of the whole production coming fro m the small-scale farmers[4]. Si tophi lus zea mai s Motsch u ls ky is a s erious p est o f economic importance in stored products worldwide[5]. The pest is so devastating and is capable of multip lying to large populations causing tremendous damage to the grain[6]. It is estimated that about 10– 40% of the total damage to stored grains wo rld wide is caused by insect pests[7] of * Corresponding author: (Simbarashe Muzemu) Published online at Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved which they account for approximately 5–10% of maize grain loss in Southern Africa[8]. Under severe infestations, maize weevils can cause up to 90% loss of stored grain[9]. Grain weight loss of 12–20% and 80% caused by the maize weevil is co mmon in untreated maize grain stored in traditional structures in tropical countries[10,11]. It has been reported that much of the maize produced by the smallholder farmers in Zimbabwe is lost to weevil attack and very little research has been done on the development of affordable alternatives wh ich offer same control levels to weevils as pesticides[6]. Although synthetic pesticides can control it, majority of co mmunal farmers are resource-poor and have no means and proper skills to acquire and handle them. Moreover, pesticides are expensive, not readily available and pose health problems to consumers due to their to xicity since many have some residual effect. Ev idence fro m different African countries illustrates that improper use of chemicals is causing loss of life and negative repercussions on human health[2]; and other problems associated with their use are loss of efficacy, regulatory restrictions as a result of adverse effect on non-targeted organisms and eco-to xicity[12,13]. The status quo is exacerbated by the development of resistance to 18 Simbarashe M uzemu et al.: Screening of Stored M aize (Zea mays L.) Varieties Grain for Tolerance A gainst M aize Weevil, Sitophilus zeamais (M otsch.) these insecticides by the pests resulting in their resurgence hence a need to the search for effective and safe variety of alternatives. Moreover, the sustainability of conventional chemicals used to preserve grain is questionable given the high level of poverty present in the rural co mmunities in Africa [14] . Decrease in agricultural productivity exposes local farmers and the nation to chronic food shortages hence it is a serious threat to mankind. This creates the need for farmers to come up with mechanisms for conserving their scarce food resource base. The constraints to maize seed availability and affordability have pro mpted the need to sow open pollinated varieties (OPVs) by resource constrained smallholder farmers in Zimbabwe. The advantages to the use of insect resistant varieties are especially important in developing countries where farmers can rarely affo rd to purchase insecticides for crop protection[15]. These varieties provide practical and economic way to min imize field and grain storage losses to improve both quantity and quality of stored grain for planting and hu man consumption [16]. Insect resistant crops greatly increase farming efficiency by reducing or eliminating the costs of insecticides and the risk of y ield losses fro m insect damages. Gra in resistance as a method of pest control is advantageous since most resistant varieties maintain h igh levels of resistance for a long time despite upsurge of biotypes[17]. The potential negative effects associated with insecticide use are eliminated with the use of insect resistant varieties. In many developing countries, the demand for maize surpasses that for other food crops due to the growth in meat and poultry consumption, which consequently, have led to the rapid increase in the demand for maize as livestock feed[18]. Thus there is a need to develop cheaper, equally effective and safer alternatives for insect pest control, including host plant tolerance[19]. However, the level of OPVs resistance or tolerance to weevil attack is not fully understood hence there is need for screening of maize grain variet ies for ma ize weevil evaluations[20]. Considering the economic importance of maize in the country as well as the destructive nature of S. zeamais to the crop, the present study was undertaken with the main objective of screening different stored maize varieties grain for tolerance against the maize weevil. 2. Materials and Methods The experiment was carried out in the Ento mology laboratory at Cotton Research Institute in Kadoma, Zimbabwe. The area is located 3 km west of Kadoma town along the Chakari road, on longitude 18°19' south and latitude 29°53' east, at an altitude of 1156 m above sea level. The area falls under natural region III of Zimbabwe’s agro-ecological zones, with an average annual temperature and rainfall o f 23– 30°C and 400– 600 mm respectively. Five pure maize open pollinated varieties namely ZM309, ZM401, ZM421, ZM521, and Hickory King obtained fro m Crop Breeding Institute, Harare and a hybrid SC709 fro m Seed-Co Zimbabwe were used in the experiment. A randomized co mp lete block design was used to arrange the jars in the laboratory to minimize the door effects and each treatment was replicated five times. The maize grain was thoroughly cleaned using a 1 mm sieve-mesh screen so as to remain with grain with intact testae, which was then disinfested by keeping it in a deep freezer at –4°C for 2 weeks. The mo isture content of the grain was in the range of 12-13%. Appro ximately 100 g of each of the maize varieties was placed into the 750 ml jars with perforated lids. One hundred three-week old unsexed adult weevils were introduced into each jar. The jars were placed in the shelves at a temperature range of 28±2°C and relative hu midity of 70±5 %. Weevils used in the experiment were obtained fro m the Crop Protection Department at the institute. Grain fro m the previous season was used to prepare the pest culture. Grain was first sieved to remove dirt and broken part icles. Three 750 ml consul jars with perforated lids to allow for air circulat ion were filled with grain to the three quarter level. Filter paper was put inside each o f the perforated lids to prevent insects fro m escaping. The jars containing the grain were placed in a freezer for 2 weeks to kill any insect eggs which might have been present in the grain. The grain was then transferred into the shelves and stored for 3 weeks to achieve uniform grain temperature and moisture content. The temperature was set at 28±2°C and humidity at 70±5%. After 3 weeks each consul jar was infested with 100 adult weevils and the jars were placed in the shelves. After 14 days oviposition period the grain was sieved to discard adult weevils wh ich had laid eggs in the kernels. Maize weev ils take about 30 days to complete their life cycle[21], so after 30 days the weevils began to emerge. After 35 days the F1 progeny was collected by sieving damaged grain. The adult weevils collected were in the range of 1−3 days old. The weevils were later used in the evaluation of OPV’s for weevil res is tan ce. A refrigerator was used for disin festations of seed by storing the seed at −40C for two weeks. Camel hair brush was used for collecting insects and the tweezers for hold ing the insects. A 1 and 4.7 mm screen meshes were used for separating grain, dust and insects. Parent weev il mo rtality was assessed 14 days after the introduction of the insects. The grain was sieved and the number of dead and live pests was counted from each jar to obtain parent weevil mo rtality. The following formu la was used to calculate the percentage weevil mortality; Parent weevil mortality number of dead pests = × 100 total number of all the pests After 14 days, the weevils which emerged fro m the grain in each jar were counted and their number was recorded. After 45 days of incubation the grain was sieved, dust removed and the clean grain was weighed and expressed as a percentage weight loss of the original weight[22]; International Journal of Plant Research 2013, 3(3): 17-22 19 Percentage grain weight loss (original weight − weight after 45 days) = × 100 original weight Forty five days after incubation, the grain was thoroughly mixed and 30 maize kernels (grains) were randomly selected to assess the level of grain damage. The grain was sorted into damaged (grain with holes and/or tunnels) and undamaged grain. Grain in each fraction was counted and the number of damaged grain recorded. Maize grain genotypes exposed to maize weev ils for 45 days was germinated in an incubator at a temperature of 28°C in Petri- d ishes in mo ist wrapping papers. Twenty seeds per maize grain genotype were placed on top of the mo ist paper in Petri- dishes. The Petri- dishes were covered and put into an incubator for 10 days at 28°C. Germination percentage was calculated using the formu la[23]; Germinantion percentag e = G1 × 100; Where G1 = G2 total germinated grain, G2 = total grain in Petri -d ish A general analysis of variance (ANOVA ) for parent weevil mortality, number of weevils emerged, percentage grain weight loss, kernel damage and percentage germination was conducted using GenStat statistical package 14th Edit ion[24]. Mean separation was done by using least significant difference (LSD) to co mpare the significant differences between the treatments at 5% level of s ig n ifican ce. 3. Results and Discussion 3.1. Parent Weevil Mortality weevil attack. High parent weevil mortality may a lso be due to antixenosis, that is, resistance mechanisms wh ich deter colonisation by the insect[26]. High parent weevil mortality might also be attributed to absence of nutritional factors in the grain which might be important for insect development[27]. Hickory King, ZM309 and ZM401 had the lowest parent weevil mortality indicating high susceptibility to weevil attack (Figure 1). 3.2. Number of Weevil Emergence There were variations and significant differences (p<0.05) were observed among the variet ies in the nu mber of weev ils which emerged. The hybrid SC709 had the highest number of weevils which emerged followed by ZM309 and ZM401 whilst ZM421 and ZM521 had the least. The mean number of weevils emerged ranged fro m 0.6-16.2 (Figure 2). The differences in the nu mber of weevils emerged showed that there existed variation in susceptibility to maize weevil attack among the varieties. The varieties which recorded the highest number of weevils emerged indicated greatest susceptibility to maize weevil attack and this might have been due to lack of resistance mechanisms in or on the grain[28]. The low weev il emergence in variet ies ZM421 and ZM521 can be attributed to high mortality of parent weevils. These parent weevils might have died before laying eggs or after lay ing few eggs thus few progeny resulted. The low weev il emergence in these varieties may possibly be attributed to absence of essential nutrients and unbalanced proportion of nutrients leading to the death of the larvae[29]. The significant variat ion for nu mber of weevils emerged among the varieties could be due to antibiosis effects in resistant varieties leading to retarded develop ment of weevil progeny and sometimes death of weev ils before laying eg gs [30 ]. Fi gure 1. Effect of different maize variet ies on weevil mort ality There were significant differences (p<0.001) among the varieties for parent weev il mortality, with ZM 421 and ZM521 reg istering the highest parent weevil mortality followed by ZM401, ZM309 and Hickory King while SC709 had the least parent weevil mortality. Mean percentage parent weevil mortality ranged fro m 2.6−24.8 (Figure 1). The highest mortality which was observed in ZM421 and ZM521 could be due to physical factors such as antibiosis or hardiness as a result of biochemical compounds which are toxic to the insects which led to subsequent death of the weevils[25]. This indicated that these two variet ies have resistant factors in or on their grain which helped to prevent Figure 2. Effect of different maize varieties on number of weevil emergence aft er 14 days of exposure 3.3. Grain Weight Loss and Damage Maize g rain weight loss and damage were highly significant (p<0.001) among the experimental varieties. Hickory King recorded the highest weight loss, followed by ZM401, ZM 309, and SC709 wh ilst ZM521 and ZM421 had the lowest weight loss (Table 1). Hickory King had the highest number of damaged grain after 45 days exposure to 20 Simbarashe M uzemu et al.: Screening of Stored M aize (Zea mays L.) Varieties Grain for Tolerance A gainst M aize Weevil, Sitophilus zeamais (M otsch.) maize weevil followed by ZM 401, SC709, ZM309 and ZM521 whilst ZM421 had the least number of damaged grains. The mean number of damaged grain ranged from 0.4−19.2 (Table 1). The researcher considered weight loss and grain damage as the most indicators of a variety’s susceptibility to weevil attack. Lo w weight loss in ZM521 and ZM421 could be due to resistance mechanisms in or on the grain which prevented weevil attack. Hicko ry King had the greatest weight loss thus could be said to be more susceptible to weevil attack than other experimental varieties. Resistance mechanisms could be in the form of deterrents which could be biochemical or morphological or a combination of both[26]. Biochemical co mpounds in the form o f phenolic amides such as defeuroyl and dicoumaroyl may be antib iosis factors to the S. zea mais[15]. These phenolic compounds have been detected by fluorescence imaging techniques which clearly show the phenolic barrier to insects in the outer tissue[15]. It has also been reported that antibiotic effects increased restlessness of insects which reduced feeding and could exp lain how grain damage and weight loss were low among resistant varieties[26]. So me researchers[27] also suggested that variation in maize hybrids was due to antibiosis. Less grain damage could be attributed to antixenosis mechanisms like a smooth pericarp which could deter weevils fro m oviposition and feeding and also prevents mandibles from gripping maize kernels. The great variation observed in the germplas m evaluated forms a genetic resource base for further imp rovement to raise the levels of resistance to S. zeamais while conserving the farmer preferred traits. This variation in response to the maize weevil attack gives is evident of genetic diversity existence hence a rich genetic resource base for breeding for resistance exists. This offers the opportunity to explo it the variab ility with the aim of reducing post-harvest insect-pest losses through genetic imp rovement[31]. This imp lies that most of the variation among the genotypes is due to their genetic make-up with litt le influence fro m the environment, suggesting that maize improvement for resistance to storage pests is possible through selection[32]. Table 1. Mean percentage grain weight loss and grain damage among different varieties aft er 45 days of exposure to S. zeamais Variety ZM521 ZM421 Hickory King ZM401 ZM309 SC709 Grand mean Fprob l.s.d % grain weight loss 0.19a 0.05a 8.35b 5.13b 4.33ab 3.9ab 3.66 0.012 4.702 No. of damaged grain 1.60a 0.40a 19.20c 12.00b 9.00b 10.20b 8.73 <0.001 6.749 3.4. Germination highest in variety ZM421 fo llowed by ZM521, ZM 309, Hickory King and ZM401 while SC709 had the least percentage germination. Mean germination percentage ranged fro m 68−96% with a mean of 80.3% (Figure 3). The observed differences in germination percentages showed that the varieties differed in susceptibility to maize weevils. ZM421 and ZM521 had the highest germination percentage indicating high ability to germinate after exposure to maize weevils. These varieties also recorded the least number of weevils emerged, highest mortality and least grain weight loss. Thus these two varieties might have resistance factors which could result in less maize weevil damage thus ability of the grain to germinate is not affected much by maize weevil attack. ZM401, Hickory King and ZM309 had low germination percentages indicating their susceptibility to maize weevil. Th is might be due to lack of resistance mechanis ms within or in the grain to protect it fro m weevil attack. Weevil damaged grain germinated and this might be attributed to the fact that the weevils did not damage the embryo. Figure 3. Effect of different maize varieties on percentage germination after exposure to S. zeamais 4. Conclusions The investigation showed that varieties had different response to maize weevil attack fro m very susceptible, moderately to tolerance. ZM 421 and ZM 521 were h ighly tolerant as evidenced by the least weight loss, grain damage, number of weev il emerged and highest parent weevil mortality and kernel germination. SC709 and ZM403 had moderate tolerant wh ile ZM 401 and Hickory King were highly susceptible. Breeding programmes should aim at breeding ZM521 and ZM421 maize weevil tolerant grain since there is evidence that some tolerant factors exist in the gene pool. OPV use leads to improved seed availab ility and ensure food security at family household level in Zimbabwe. ACKNOWLEDGEMENTS Significant differences (p<0.05) were observed among the The authors would like to acknowledge the management treatments. Percentage germination after weevil attack was of Cotton Research Institute, with special grat itude to the International Journal of Plant Research 2013, 3(3): 17-22 21 Ento mology Depart ment personnel for allo wing the experiment to be carried out in their laboratory. [15] M ihm JA (ed). 1997. Insect Resistant maize, Recent Advances and Utilization: Proceedings of an International Symposium held at the International M aize and Wheat Improvement Centre (Commit) 27 November – 3 December1994,DF : Cimmyt, M exico. REFERENCES [1] Rukuni M , Tawonezvi P and Eitcher C. 2006. Zimbabwe’s Revolution Revisited. Sable Press Private Limited, Zimbabwe. [2] FAO. 2003. The Status of Food Production in Zimbabwe, Global Early Warning Unit, M inistry of Lands and Agriculture, Harare. [16] Issa US, Afun JVK, M ochiah M B, Owusu – Akyaw M and Braimah H. 2011. 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