Prof. Nantakorn Boonkerd

Year	Title	Journal
1988	Iron‐deficiency specifically limits nodule development in peanut inoculated with Bradyrhizobium sp. O'HARA G.W., DILWORTH M.J., BOONKERD N., PARKPIAN P.	New Phytologist
Abstract: Severely iron‐deficient peanuts (Arachis hypogaaea L.) grown on calcareous soils in central Thailand failed to nodulate until given foliar iron applications. Glasshouse experiments were conducted on two cultivars (Tainan 9 and Robut 33–1) to identify which stage of the nodule symbiosis was most sensitive to iron‐deficiency. Iron‐deficiency did not limit growth of soil or rhizosphere populations of peanut liradyrhizobium. Similar numbers of root nodule initials formed in the roots of both control and iron‐sprayed plants, showing that iron‐deficiency did not directly affect root infection and nodule initiation. Plants sprayed with iron produced greater numbers of excisable nodules and carried a greater nodule mass than untreated plants. Five days after iron application, nodules on sprayed plants of CV. Tainan 9 contained 200–fold higher bacteroid numbers per unit weight and 14–fold higher concentrations of leghaemoglobain. The onset of nitrogenase activity was also delayed by iron deficiency in both cultivars. Tainan 9 appeared more sensitive to iron‐deficiency than Robut 33‐1 in terms of nodule mass produced, but both cultivars showed the same effect of iron‐deficiency on nitrogenase activity per plant. It is concluded that the failure of the infecting rhizobia to obtain adequate amounts of iron from the plant results in arrested nodule development and a failure of nitrogen fixation. Copyright © 1988, Wiley Blackwell. All rights reserved Keyword: Aratahis hypogaea; bacteroids; iron‐deficiency; leghaemoglobain; nitrogen fixation Scopus Link: https://www.scopus.com/inward/record.uri?eid=2-s2.0-84982619755&doi=10.1111%2fj.1469-8137.1988.tb00203.x&partnerID=40&md5=d857f54ebd9e49db9fe60738a09d96b5 DOI: 10.1111/j.1469-8137.1988.tb00203.x
1988	Nitrogen Fixation (N-15 Dilution) with Soybeans Under Thai Field Conditions. III. Effects of Bradyrhizobium Japonicum Strains and Herbicides in Northeast Thailand Kucey R.M.N., Chaiwanakupt P., Snitwongse P., Boonkerd N., Siripaibool C., Rungrattanakasin W., Wadisirisak P., Toomsan B., Rennie R.J.	Journal of General and Applied Microbiology
Abstract: In the infertile sandy soils of northeast Thailand, field experiments were conducted to evaluate the effects on rates of biological nitrogen fixation (BNF) of inoculating soybeans with selected strains of Bradyrhizobium japonicum and adding herbicides. Inoculating soybean seeds with effective B. japonicum strains increased the acetylene reduction by nodulated root systems, and increased the nodule numbers and dry weights associated with soybean roots. The amounts of N2 fixed, as measured by N-15 isotope dilution methods, were also increased by adding the B. japonicum. Inoculation of soybeans with a nif– strain of B. japonicum resulted in increased nodule weights and numbers, but did not increase the acetylene reduction rates or the amounts of N2 fixed. There was a significant strain-cultivar interaction. Application of metolachlor, alachlor, fluazifop butyl or sethoxydim did not reduce the levels of N2 fixed by B. japonicum in association with soybeans, but paraquat did significantly reduce the N2 fixed by the inoculated plants. © 1988, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved. Keyword: Scopus Link: https://www.scopus.com/inward/record.uri?eid=2-s2.0-0344386134&doi=10.2323%2fjgam.34.243&partnerID=40&md5=adf4f677a9ca0632aabbae48d67cc829 DOI: 10.2323/jgam.34.243
1987	POPULATIONS OF BRADYRHIZOBIUM JAPONICUM IN FIELDS CROPPED WITH SOYBEAN-RICE ROTATIONS. Weaver R.W., Morris D.R., Boonkerd N., Sij J.	Soil Science Society of America Journal
Abstract: The population density of Bradyrhizobium japonicum in soil, before planting, largely determines the potential yield increase of soybeam (Glycine max L. Merrill) due to inoculation. Soybean is cultured in rotation with rice (Oryza sativa L. ) in the paddy rice belt of the southern USA. Nineteen fields were sampled to determine the influence of paddy rice culture on the population of B. japonicum. Populations in fields following soybean were approximately 1 plus 104 bradyrhizobia g minus 1 soil. Growing rice after soybean did not reduce the population of bradyrhizobia. Apparently the bradyrhizobia were able to survive the conditions in saturated soil for several months. Keyword: Scopus Link: https://www.scopus.com/inward/record.uri?eid=2-s2.0-0023147013&doi=10.2136%2fsssaj1987.03615995005100010019x&partnerID=40&md5=34d0b187896ce5aa8f426f8e4582e896 DOI:** 10.2136/sssaj1987.03615995005100010019x
1985	Effects of post-emergence inoculation on field grown soybeans Boonkerd N., Arunsri C., Rungrattanakasin W., Vasuvat Y.	MIRCEN Journal of Applied Microbiology and Biotechnology
Abstract: Inoculation of soybean seed with rhizobia has traditionally been performed by applying the inoculum to seed immediately before planting. In some conditions, however, the application of rhizobia to seed may fail to give satisfactory nodulation. The hypothesis that such failure of seed inocuation might be remedied by inoculating field grown soybeans after planting (post-emergence inoculation) was tested at three locations which were free from native soybean rhizobia. Post-emergence inoculation treatments comprised inoculation at five, 10, 15 and 20 days after planting. The inoculation technique consisted of suspending peat-based inoculant at the recommended rate in water, and pouring this suspension over the planted rows. Satisfactory nodulation and plant growth were obtained following inoculation at five, 10 and 15 days after planting in the two areas where surface soil moisture was adequate. In another area where the soil surface was relatively dry at the time of inoculum application, nodulation was greatly reduced. Nodules formed following post-emergence inoculation were located mainly on lateral roots near the soil surface. Inoculation at 20 days after planting was, however, unsuccessful. With good rainfall seed yield obtained from seed-inoculated plants was not significantly different from those that were obtained from plants inoculated five or 10 days after planting. It seems, therefore, that failures of seed inoculation can be corrected by post-emergence inoculation within two weeks of planting, provided that surface soil moisture is adequate. © 1985 Oxford University Press. Keyword: Scopus Link: https://www.scopus.com/inward/record.uri?eid=2-s2.0-34250119867&doi=10.1007%2fBF01742580&partnerID=40&md5=778b11a81d297b25fb7908757753fa9b DOI: 10.1007/BF01742580
1982	Cowpea rhizobia: Comparison of plant infection and plate counts Boonkerd N., Weaver R.W.	Soil Biology and Biochemistry
Abstract: Enumeration of Rhizobium in soil is usually accomplished by the most probable number (MPN) plant infection method. The accuracy of MPN counts as compared to plate counts was determined for five strains of cowpea rhizobia. Host plants included cowpea (Vigna unguiculata (L.) Walp.), siratro (Macroptilium atropurpureum (DC.) Urb.) and peanut (Arachis hypogaea L.). Plastic growth pouches were used primarily for cowpea and siratro while plastic cups containing vermiculite were used for peanut. The number of rhizobia determined by the MPN method using cowpea, siratro and peanut underestimated the population from 10- to 100-fold. A control experiment using soybeans (Glycine max (L.) Merrill) indicated that the MPN method was accurate for R. japonicum. Experimentors using the MPN method should be aware of its accuracy for particular Rhizobiutn-legume combinations. © 1982. Keyword: Scopus Link: https://www.scopus.com/inward/record.uri?eid=2-s2.0-0020467623&doi=10.1016%2f0038-0717%2882%2990042-6&partnerID=40&md5=a5a06f49be7247369076f686a8493191 DOI: 10.1016/0038-0717(82)90042-6
1982	Survival of cowpea rhizobia in soil as affected by soil temperature and moisture Boonkerd N., Weaver R.W.	Applied and Environmental Microbiology
Abstract: [No abstract available] Keyword: Scopus Link: https://www.scopus.com/inward/record.uri?eid=2-s2.0-0020071212&doi=10.1128%2faem.43.3.585-589.1982&partnerID=40&md5=d2fc10692dae97faa4c7a1d8ff217b5c DOI: 10.1128/aem.43.3.585-589.1982
1980	Effects of N-serve on soybeans and soil nitrogen transformations Morris D.R., Boonkerd N., Vasuvat Y.	Plant and Soil
Abstract: Plant dry weight, total N, and total Ca was increased at 0.1 and 1 ppm N-serve. At greater 10 ppm the plants showed visual symptoms of a stunted growth, stem elongation, flowers, and pods failed to form or were aborted, young leaves were curled, and roots were club shaped with many branches. These symptoms were increasingly evident with increasing N-serve application rates. The reason was attributed to an auxin effect. Dry wt and total N in the plant was less than the control at the higher N-serve applications. There was little effect on nitrogenase activity at less than 10 ppm N-serve. Nodulation tended to increase at 0.1 and 1 ppm N-serve. Nitrification was inhibited up to 104 days at 20 ppm N-serve. The soil pH of the high N-serve rates was decreased at 104 days probably due to nitrification. Generally there were little detectable differences among treatments in soil organic N. The average soil organic N from 0 to 104 days decreased by 0.01%. Average increase in total N within each pot at harvest was equivalent to about 138 kg N/ha. © 1980 Martinus Nijhoff Publishers. Keyword: Auxin; Glycine max(L.) Merr.; N fixation; N-serve; Soil N Scopus Link: https://www.scopus.com/inward/record.uri?eid=2-s2.0-10544249431&doi=10.1007%2fBF02139639&partnerID=40&md5=63c740fe09edc6b053739101260ff990 DOI: 10.1007/BF02139639