Cassava (Manihot esculenta Crantz) is a major tuberous crop produced worldwide. In this study, we sequenced 158 diverse cassava varieties and identified 349,827 single-nucleotide polymorphisms (SNPs) and indels. In each chromosome, the number of SNPs and the physical length of the respective chromosome were in agreement. Population structure analysis indicated that this panel can be divided into three subgroups. Genetic diversity analysis indicated that the average nucleotide diversity of the panel was 1.21 × 10-4 for all sampled landraces. This average nucleotide diversity was 1.97 × 10-4, 1.01 × 10-4, and 1.89 × 10-4 for subgroups 1, 2, and 3, respectively. Genome-wide linkage disequilibrium (LD) analysis demonstrated that the average LD was about ∼8 kb. We evaluated 158 cassava varieties under 11 different environments. Finally, we identified 36 loci that were related to 11 agronomic traits by genome-wide association analyses. Four loci were associated with two traits, and 62 candidate genes were identified in the peak SNP sites. We found that 40 of these genes showed different expression profiles in different tissues. Of the candidate genes related to storage roots, Manes.13G023300, Manes.16G000800, Manes.02G154700, Manes.02G192500, and Manes.09G099100 had higher expression levels in storage roots than in leaf and stem; on the other hand, of the candidate genes related to leaves, Manes.05G164500, Manes.05G164600, Manes.04G057300, Manes.01G202000, and Manes.03G186500 had higher expression levels in leaves than in storage roots and stem. This study provides basis for research on genetics and the genetic improvement of cassava.

[Purpose] Our aim was to analyze the cause of yield gap and its limiting factors of cassava,and then to explore measures to narrow the gap.[Method] The yield gap of cassava both in Wuming and Hepu Counties of Guangxi Province was studied in this research.[Results] The results showed that average planting density and continuous cropping years of 25％ the lowest yield farmer were significantly higher than those of other farmers.Only 25％ the highest yield farmers' N,P2O5,K2O ratios were fitted for recommended fertilization ratio of long-term fertilization trial,and the other farmers' N,K2O ratios were lower than this ratio,also 25％ the highest yield farmers' K2O applications were significantly higher than those of the other farmers.More than 45％ farmers had excessive fertilization,the average saving amount of fertilizer was 127.50 kg/hm2,the saving potentials of phosphate,potassium and nitrogen fertilizer were 43.58％,16.26％,15.00％,respectively.The fertilizer efficiency was low,only 4.26％-6.32％ farmers reached a high yield and high efficiency.The investment/yield ratio reached the maximum when the yield reached 79.63 t/hm2,after that,it showed diminishing returns with the increasing of yield.The cost of labor,especially spending on the harvest and management was the main limiting factors for yield gap.[Conclusion] Therefore,we have four suggestions for narrowing the yield gap of cassava.(1) Reasonable planting density.(2) The years of continuous cropping should not be more than three years.(3) The principles of fertilizer application should be in accordance with "tiny adjustment based on fertilization formula" and "if that longer continuous year of cropping is,the ratio of nitrogen and potassium fertilizer is higher",it recommending that,more nitrogen fertilizer and potassium fertilizer in basic fertilization,less nitrogen fertilizer and more potassium fertilizer in top-dressing fertilization,and to decrease phosphorus fertilizer and control nitrogen fertilizer and also potassium fertilizer in total could be effective nutrient management.(4) The input-output ratio should be promoted,and advanced mechanization replacing for labor should be spread in all cassava production.

Taking Holland 15 as the test material,we studied the effects of different application rates and proportions of nitrogen fertilizer and potassium fertilizer on the plant growth characteristics and yield of winter potato which was cultivated by black film interlayer covering.The results showed that different application rates and proportions of nitrogen fertilizer and potassium fertilizer had no effects on seedling emergence speed,eventual seedling rate,and total number of leaves.However,the plant height increased with the increase of nitrogen fertilizer application rate,while decreased with the increase of K2O application rate.When the application rate of K2O increased,the diameter of main stem showed a rising trend.When the application rate of nitrogen was below 225 kg/hm2,the yield of potato increased with the increase of potassium fertilizer application rate.When the application rate of nitrogen reached 300 kg/hm2,the yield of potato decreased with the increase of potassium fertilizer application rate.These results showed that the fertilization quantity should not be higher than N 300 kg/hm2+K2O 150 kg/hm2.The highest yield was obtained when N 225 kg/hm2+K2O 450 kg/hm2 were applied.

6 demonstration bases for the models of cassava intercropped or interplant were built in Wuming County,Guangxi Province,P.R.China in 2009.the analytical results of yield and benefit showed that: compare with single cassava model(CK),water melon,pumpkin,muskmelon or hair melon interplant cassava,and cassava intercropped peanut or soybean improved 6.1%-25.2% cassava fresh root yield than CK;1.6-4.2 times total income of CK;1.7-4.9 times net income of CK.Interplant model of melon were high benefit than the intercropped model of peanut or soybean.Above model were 16 800 hm2 planted area and occupied 60% in whole Wuming county in 2009.

制订广西区武鸣县香瓜、毛节瓜套种木薯的生产技术规程,从选地整地、选择品种、育苗、施肥、定植、盖拱棚、揭膜通风降温、水分管理、引蔓压蔓、整枝留瓜、保花保瓜、防治病虫害等方面对香瓜及毛节瓜栽培管理进行了规范,从选择品种、种茎处理、种植、补苗间苗、中耕除草、追肥、防治木薯朱砂叶螨等环节对套种木薯的栽培管理进行了规范.

This article summarized the high-yielding and high-benefit cultivation model of cassava which was interplanted by water melon or pumpkin,based on many years' practice and exploration in Wuming county of Guangxi.The economic benefit of interplanting water melon and cassava was 210% higher than that of only planting cassava,and the economic benefit of interplanting pumpkin and cassava was 160% higher than that of only planting cassava.