Crop Diversity for Ecological Disease Control in Potato and Maize

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1 March, 200 Journal of Resources and Ecology J. Resour. Ecol. 200 ()45-50 DOI:0.3969/j.issn x Crop Diversity for Ecological Disease Control in Potato and Maize HE Xiahong, ZHU Shusheng, WANG Haining, XIE Yong, SUN Yan, GAO Dong, YANG Jing, LIU Lin, LI Qixin 2, ZHANG Shaobo 2, ZHAO Gaohui 3, HU Mingcheng 3, JIANG Kaimei, LI Chengyun and ZHU Youyong Key Laboratory of Agro-Biodiversity and Pest Management of Education Ministry of China, Yunnan Agricultural University, Kunming 65020, Yunnan, China; 2 Agricultural Technology Extension Centre of Xuanwei City, Xuanwei City, , Yunnan, China; 3 Agroscience Research Institute of Zhaotong City, Zhaotong , Yunnan, China Abstract: Aiming at the difficulties of controlling on potato late blight, maize northern and southern leaf blight diseases caused by the overlapping of rainfall and peak of these diseases in mountainous area of Southwest China, intercropping of potato with maize by adjusting planting time and spacing to avoid rainfall and disease occurrence was assessed. The results showed that early or late planting of potato, avoiding rainfall peak from potato vigorous growth and increasing light and air diffusion in space, alleviated potato late blight disease. The average severities decreased by 44.3% for potato late blight, 4.8% for maize northern leaf blight and 22.5% for maize southern blight, compared with the monocropped controls. Moreover, this kind of intercropping pattern improved the output significantly. The crop yields were increased and reached a land equivalent ratio (LER) of.738 for early planting pattern and.766 for late planting. This approach can be practical significance for ecological control of crop disease and food production increase. The agroecological structure in harmony with the natural environment results in ecological and cycle agriculture with high yield, high quality and high efficiency. Key words: crop diversity; agroecology; intercropping; potato late blight disease; maize northern leaf blight; maize southern leaf blight It has been recognized that reduction in arable land is one of the key factors in causing the current food crisis (Fischer et al. 2002). Modern agricultural systems exhibit a poorly structured assemblage of farm components. High degree of management and large inputs of artificial fertilizers, pesticides, fungicides and herbicides for the purpose of higher yields resulted in degradation of agroecosystem, which finally affected food safety and farmers income (Ross 2009). In China, rich traditional experiences had been accumulated in long-term practices of agricultural production. Theses experiences significantly promote ecological protection and sustainable socio-economic development in rural areas (Li 2009). The techniques of crop diversity for yield increase and disease control had been widely adopted in Southwest China (Li et al. 2009). In this study, potato was intercropped with maize, diseases of potato and maize were assessed after ecological management in southwest mountainous area of China. Most researches had been made on potato late blight (Phytophthora infestans), maize northern leaf blight (Setosphaeria turcica) and southern leaf blight (Bipolaris maydis) diseases in the world. However, they are still devastating diseases and difficult to control (Reader 2009; Wang et al. 2005; Liu & Yu 998). May to September is the routine cropping season for hundreds of years in Southwest China (Sun et al. 2008). Potato and maize are planted in mid-may and harvested in September. Monsoon climate makes rainfall concentrated in June to October. Especially about 60% of annual rainfall is during July to September in this mountainous area (Liu & Yu 998). Therefore, potato and maize diseases break out easily during the vigorous growth stage under continuous raining and low lumination in August (Wang et al. 2005; Liu & Yu 998; Sun et al. 2008). The infection and development of diseases are favoured by warm, showery and humid weather (Perkin et al. 987), which occurs every year and causes significant yield losses and economic damage in Yunnan Province (Wang et al. 2005; Song et al. 996). So far, Received: Accepted: Corresponding authors: ZHU Youyong. yyzhu@ynau.edu.cn; HE Xiahong. hexiahong@googl .com.

2 46 there is no effective method for these diseases control. Resistant hybrids, rotation and chemical control are normally used to combat these diseases (Haverkort et al. 2008; Pilet et al. 2006; Nærstad & Hermansen 2006; Pratt et al, 2003; Byrnes et al. 989). Chemicals applied can be easily washed out by the rain (Kromann et al. 2009) and there is no resistant variety available (Byrnes et al. 989; Pataky et al. 998). New technique for ecological control of late blight disease is urgently needed by local farmers and food safety production (Morgado & Willey 2008; Garrett et al. 200; Thrupp 2000). Materials and methods. Materials Potato varieties of Hui-2 and Hezuo88 and maize varieties of Huidan4 and Xuanhuangdan were selected for the field experiments. Their yields, potato resistances to late blight disease maize resistances to northern and southern leaf blight disease were showed in Table. Potato seeds were sprayed and mixed thoroughly by 400 of 58% metalaxyl-mancozeb before planting. Coated maize seeds were used..2 Experiment plots design.2. Experiment for intercropping of potato early planted before maize was carried out in Zhaotong and Xuanwei cities of Yunnan Province in 2006 and Three treatments for each potato variety included one potato monoculture, one maize monoculture and one intercropping by early intercropped potato with maize, i.e. potato was early planted on March 2 and maize cultivation followed the usual time frame sown on May 8. For monocropping, potato and maize were grown on May 8. Maize variety was Huidan4. Planting arrangement in plots were patterned after those used by local farmers. Two rows of potato intercropped with 2 rows of maize of.8m were as one strip. Rows spacing were 60cm and plants spacing were 25cm for potato; 50cm and 20cm for maize; Distance between potato and maize were 35cm; 60cm row Journal of Resources and Ecology Vol. No., 200 spacing and 50cm plants spacing for potato monocultures, 50 cm and 40cm for maize monoculture (Fig. )..2.2 Experiment for potato late planted after maize was in Luliang County and Xuanwei City of Yunnnan Province in 2007 and Three treatments for each potato variety included two monoculture of potato and maize and one intercropping by late intercropped potato with maize, i.e. maize were sown at the same time as above May 8, potato was late planted on August 5. For monocropping, potato and maize were grown on the same day as above May 8. Maize variety was Xuanhuangdan. Two rows of potato intercropped with 2 rows of maize. Spacings and arrangements were the same as above (Fig. ). A total of 8 plots for each experiment consisted of 3 treatments for each potato variety, 3 replicates for each treatment. Each treatment (plot) was 50m 2..3 Disease investigation Detailed examination and rating were done for potato late blight, maize northern leaf blight and southern leaf blight. The disease estimation of potato late blight (Phytophthora infestans [Mont.] de Bary) followed Handbook of Crop Pest Forecasting (2006); Maize northern leaf blight (Setosphaeria turcica Leonard) is based on the NY/ T , P. R. China (2007); Maize southern leaf blight (Bipolaris maydis [Nisikado et Miyake] Shoem) is based on the NY/T , P.R. China (2007). All investigated diseases were assessed at five sampling points in each plot, distributed in a uniform pattern. Disease severity was summarized within each plot as {[(n ) + (n 2 2) + (n 3 3) + + ( n N N)]/N ( n + n 2+ n 3+ + n N)} 00, where n... n N is the number of leaves in each of the respective disease categories, N is the highest scoring of the disease; n=3. Statistical analyses were conducted by software SPSS 3.0. All differences between pairs are significant at P 0.05 based on one-tailed t-test (Zhu et al. 2000)..4 Yield and monetary value survey Crop yield was determined by grain weight for maize and fresh tuber weight for potato and were based on actual mean plot yields and for individual species within intercropping. Crop values were based on market prices in different year (Ministry of Agriculture of the People s Republic of China 2007; Zhu et al. 2000)..5 Land equivalent ratio assessment Land equivalent ratios (LERs) were calculated as (yield of potato in intercropping /yield of potato in monocul-

3 HE Xiahong, et al.: Crop Diversity for Ecological Disease Control in Potato and Maize 47 Table Resistances and yields for different potato and maize varieties. Greenhouse inoculation Field investigation Crops Varieties Incidence (%) Severity Incidence (%) Severity Yields (kg ha - ) Potato Hui Hezuo Maize Huidan Xuanhuangdan Table 2 Disease severity for early planting of potato before maize (mean±s.e.m). Potato Maize Hui-2 Hezuo88 Huidan4 Late blight disease Late blight disease Northern leaf blight Southern leaf blight Year Treatments Incidence (%) Severity Incidence (%) Severity Incidence (%) Severity Incidence (%) Severity 2006 intercropping 28.3± ± ± ± ± ± ± ±0.006 monocropping 64.2± ± ± ± ± ±0.0.2± ± intercropping 35.2± ± ± ± ± ± ± ±0.006 monocropping 55.4± ± ± ± ± ± ± ±0.006 Table 3 Crop yields and monetary value for early planting of potato before maize (mean±s.e.m). Yields (t ha - ) Monetary value (US $ ha - ) Treatments Crops Varieties Intercropping Potato Hui-2 8.7± ± Maize Huidan4 9.27± ± Total Monocropping Potato Hui ± ± Maize Huidan4 0.7± ± Intercropping Potato Hezuo ± ± Maize Huidan4 9.5± Total Monocropping Potato Hezuo ± ± Maize Huidan4.3± ± Crop values were based on market prices of and US$ per ton for maize, and US$ per ton for potato, respectively in 2006 and ture) + (yield of maize in intercropping/yield of maize in monoculture) (Zhu et al. 2000)..6 Date analyses Statistical analyses were conducted by software SPSS 3.0. One-tailed t-tests were used to determine if the data differed significantly (p 0.05) (Li et al. 2009; Zhu et al. 2000). 2 Results 2. Intercropping of potato early planted with maize were tested The results show that severity of potato late blight in the intercropping system was decreased by 55.2 and 44.7% in 2006 and 2007, respectively for variety Hui-2 and by 5.2% and 48.4 % respectively for variety Hezuo88 (Table 2). The severity of maize (Huidan4) northern leaf blight in the intercropping system was decreased by 9.% and 2.% in two years, respectively, and that of southern leaf blight was decreased by 25% and 40%. The average potato yields from monocrops were t ha in 2006 and 2007, and that of intercropped potato from early planting pattern were 8.72 t ha, which is 85.0% of monocropped potato (Table 3). The average yields from monocrops were 0.64 t ha for maize in these two years and that of intercropped maize were 9.45 t ha, which is 88.82% of monocropped potato. The yields for maize and potato were increased by early planting potato with maize compared with the equal areas of monocrops, which boosted the output per area. 2.2 Potato late planted with maize was also intercropped The severity of potato late blight disease in the intercrop-

4 48 Journal of Resources and Ecology Vol. No., 200 Table 4 Disease severity for late planting of potato after maize (mean±s.e.m). Potato Maize Hui-2 Hezuo88 Xuanhuangdan Late blight disease Late blight disease Northern leaf blight Southern leaf blight Year Treatments Incidence (%) Severity Incidence (%) Severity Incidence (%) Severity Incidence (%) Severity 2007 intercropping 37.± ± ± ± ± ±0.0 9.± ±0.006 monocropping 6.2± ± ± ± ± ± ± ± intercropping 34.5± ± ± ± ± ± ± ±0.006 monocropping 53.3± ± ± ± ± ± ± ±0.006 Table 5 Crop yields and monetary value for late planting of potato after maize (mean±s.e.m). Yields (t ha - ) Monetary value (US $ ha - ) Treatments Crops Varieties intercropping Potato Hui-2 5.6± ± Maize Xuanhuangdan 0.2± ± Total monocropping Potato Hui ± ± Maize Xuanhuangdan 0.5± ± intercropping Potato Hezuo ± ± Maize Xuanhuangdan 9.9± ± Total monocropping Potato Hezuo ± ± Maize Xuanhuangdan 0.3± ± Crop values were based on market prices of and US$ per ton for maize, and US$ per ton for potato, respectively in 2007 and ping system was decreased by 36.8% and 40.6% in 2007 and 2008, respectively for variety Hui-2 and by 42.4% and 35.5 % respectively for variety Hezuo88 (Table 4). The severity of maize (Xuanhuangdan) northern leaf blight in the intercropping system was decreased by 3.3% and 5.8%, respectively over two years and that of southern leaf blight was decreased by 0 and 25%. The average potato yields from monocrops were 2.62 t ha in 2007 and 2008 and that of intercropped potato yields from late planting pattern were 7.0 t ha, which is 78.68% of monocrops (Table 5). The average maize yields from monocropping were 0.3 t ha in these two Monthly rainfall (mm) Fig.2 Curves of rainfall and late blight disease occurring in 2004 in Jing an Town of Zhaotong in Yunnan Province. years and that of intercropped maize yields were 0.0 t ha, which is 97.96% of monocropped potato. The result showed that there was no significant effect on maize yields by late planting of potato with maize and intercropping resulted in an additional potato yield. 3 Discussion 3. Potato intercropped with maize by early planting and late planting of potato showed less disease occurred because of avoiding rainfall season during potato vigorous growth stage. The relationship between rainfall and potato late blight disease occurrence in Southwest China which showed disease occurrence was positively correlated with of rainfall (Fig.2), which supported that climate is the most important factor for potato late blight occurring (Pataky et al. 998; Tan et al. 200; Ding et al. 2005). High humidity in the field because of continuous rainfall from July to September was the key reason for late blight disease prevalence. The reduction in potato late blight disease in intercropped plots may be a result of less rainfall during the growing period between April and July compared with the monocrops between June and August, when the disease normally peaks. The results showed that average severity of potato late blight was decreased 49.8% and 38.8%, respectively in the intercropping systems of potato early and late planted with maize. Because

5 HE Xiahong, et al.: Crop Diversity for Ecological Disease Control in Potato and Maize 49 Table 6 Days of relative humidity in the field from July to September. Days of RH (d) in 2006 Days of RH (d) in 2007 Treatments 00% 90% 00% <80% 00% 90% 00% <80% Early planting Monocropping Late planting Monocropping Table 7 Land equivalent ratios for crop yields produced by intercropping. Treatments Crops First year Second year Early planting Potato/maize Late planting Maize/potato of the beneficial effects, this kind of intercropping design has been adopted by most of the local farmers. 3.2 After potato was harvested in the early planting pattern, the ambient humidity decreased because of the distance between the rows of maize plants. Same happened with late plating pattern. Intercropping potato and maize may benefit crop growth by increasing light and air diffusion and limiting disease spread. The observed microclimate date showed that days for 00% relatively humidity between July and September decreased 57.% and 72.7%, respectively in 2006 and 2007 in the intercropping pattern of early planting and 36.4 and 53.3% in late planting (Table 6). Average severity of maize northern and southern leaf blight diseases decreased by 20.% and 32.5% in early planting pattern and 9.6% and 2.5% in late planting pattern, respectively. 3.3 The combination of potato with maize took advantage of their different height and planting time, which significantly improved the crop yield. The intercropping resulted in the formation of three-dimensional crop assemblies in the fields, possibly improving growth through a more favorable microclimate. The results showed that the yields were increased in both intercropping patterns with LER of.739 and.736, respectively in the intercropping pattern of early planting in 2006 and 2007;and with LER of.747 and.785 in late planting in 2007 and 2008 (Table 7). 3.4 Long-term single plant species cultivation in large-scale represents an extreme example of agroecosystems with low diversity, resulting in agroecological environment getting worse and worse. Such systems are more susceptible to weather disasters, pest or disease outbreaks, chemicals abuses and even other catastrophes. In contrast, many natural ecosystems appear to be more stable in populations of their component organisms (Tilman et al. 2006). At present, most researches had highlighted biodiversity for crop pest control, higher diversity and more stability in farmland, agrobiodiversity conservation, sustainable agriculture development and agroecosystems stability enhancement (Tilman et al. 2006; Li et al. 2007). The techniques described in the paper, by adjusting the planting time of potato, not only water resources were fully used for crop growth, but also rainy season peaks were avoided and crop diseases were ecological controlled. Moreover, food productions were increased and the use of fungicides decreased. They are modern applications of traditional agriculture, providing an example for cycle agriculture and ecological agriculture to promote sustainable agriculture and rural development. References Byrnes K J, Pataky J K, White D G Relationships between yield of three maize hybrids and severity of southern leaf blight caused by race O of Bipolaris maydis. Plant diseases, 73(0): Ding J, Zheng T, Ma S, Shen H, Song B Summary of the research in potato late blight occurrence factors. Chinese Agricultural Science Bulletin, 2(2): (in Chinese) Fischer G, H van Velthuizen, M Shah, F Nachtergaele Global agroecological assessment for agriculture in the 2st century. 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