Timper P, Holbrook C, Wilson D
SUSDA ARS, P.O. Box 748, Tifton, GA 31793, USA.
Commun Agric Appl Biol Sci. 2007;72(3):655-8.
Aflatoxins are potent carcinogens produced by some Aspergillus spp. Infection of peanut (Arachis hypogaea) by root-knot nematodes (Meloidogyne arenaria) can lead to an increase in aflatoxin contamination of kernels when the plants are subjected to drought stress during pod maturation. It is not clear whether the increased aflatoxin contamination is primarily due to greater invasion of the galled pods by toxigenic Aspergillus spp. or whether root galling is also involved. Our objective was to determine the contribution of root and pod galling caused by root-knot nematodes to the increase in aflatoxin contamination in peanut. Two greenhouse experiments were conducted in which pods and roots were physically separated. Pod set was restricted to soil-filled pans (41 cm dia. x 10 cm depth), while the roots grew underneath the pan into a pot. The experiments had a factorial arrangement of treatments: pod zone with and without nematodes, and root zone with and without nematodes. In Experiment 1, 5000 eggs of M. arenaria were added to the root zone14 days after planting (DAP) and 8000 eggs were added to the pod zone 60 and 80 DAP. In Experiment 2, 3000 eggs were added to the root zone 30 DAP and 8000 eggs were added to the pod zone every week starting 60 DAP. The four treatment combinations were replicated 10 to 13 times. Conidia of Aspergillus flavus/A. parasiticus was added to the soil surface (pods zone) at mid bloom. Plants were subjected to drought stress 40 days before harvest. In Experiment 1, adding nematodes to the pod zone had no effect on aflatoxin concentrations in the peanut kernel. However, the lack of an effect may have been to due to the low occurrence of galling on the hulls. In pots where nematodes were added to the root zone, 50 to 80% of the root system was galled. Adding nematodes to the root zone increased aflatoxin concentrations in the peanut kernels from 34 ppb in the control to 71 ppb. In Experiment 2, there was heavy pod galling with galls present on 53% of the pods. Adding nematodes to the pod zone increased aflatoxin concentrations in the kernels from 19 ppb in the control to 572 ppb. Based on the results of the two experiments, it appears that infection of either the roots or pods by M. arenaria can lead to greater aflatoxin contamination of peanut kernels.
黄曲霉毒素是由某些曲霉菌种产生的强效致癌物。花生（落花生）受到根结线虫（南方根结线虫）感染后，若在荚果成熟期间植株遭受干旱胁迫，会导致果仁黄曲霉毒素污染增加。目前尚不清楚黄曲霉毒素污染增加主要是由于产毒曲霉菌种对虫瘿荚果的侵染增加，还是根结也起了作用。我们的目标是确定根结线虫引起的根和荚果虫瘿对花生黄曲霉毒素污染增加的影响。进行了两项温室试验，将荚果和根进行物理分离。荚果生长在装满土壤的平底锅中（直径41厘米×深度10厘米），而根在平底锅下方延伸到花盆中。试验采用析因设计处理：荚果区有无线虫，根区有无线虫。在试验1中，种植后14天（DAP）向根区添加5000粒南方根结线虫卵，在60和80 DAP时向荚果区添加8000粒卵。在试验2中，30 DAP时向根区添加3000粒卵，从60 DAP开始每周向荚果区添加8000粒卵。四种处理组合重复10至13次。在盛花期向土壤表面（荚果区）添加黄曲霉/寄生曲霉分生孢子。收获前40天对植株进行干旱胁迫。在试验1中，向荚果区添加线虫对花生仁中的黄曲霉毒素浓度没有影响。然而，没有影响可能是由于果壳上虫瘿发生率低。在向根区添加线虫的花盆中，50%至80%的根系出现虫瘿。向根区添加线虫使花生仁中的黄曲霉毒素浓度从对照的34 ppb增加到71 ppb。在试验2中，荚果虫瘿严重，53%的荚果上有虫瘿。向荚果区添加线虫使果仁中的黄曲霉毒素浓度从对照的19 ppb增加到572 ppb。根据两项试验的结果，似乎南方根结线虫对根或荚果的感染都可导致花生仁黄曲霉毒素污染增加。
