The basis for differential allelopathic potentials among sorghum (Sorghum bicolor L. Moench) hybrids was investigated by conducting quantitative and qualitative studies of their phenolic contents. Total phenolic content in sorghum plant parts varied within hybrids, among hybrids, and between growing seasons. Inhibition of wheat (Triticum aestivum L.) radicle growth was positively associated (r=0.66) with concentrations of total phenolics contained in plant parts. Extracts from culms contributed the higherst proportion of toxicity from sorghum plants, inhibiting radicle growth up to 74.7%. Concentrations of five phenolic acids,p-hydroxybenzoic (POH), vanillic (VAN), syringic (SYR),p-coumaric (PCO), and ferulic (FER), differed in all plant parts of the three sorghum hybrids. Concentrations of POH, VAN, and SYR were consistently higher than PCO and FER. PCO and FER wer absent from some plant parts, with FER being the most frequently missing. Inhibition of wheat radicle growth was found to be positively associated with the concentration of each phenolic acid. Vanillic acid was most highly associated (r=0.44) with inhition. Thus, above-ground sorghum tissues contained phenolic acids that contributed to allelopathic potential. Additionally, sorghum roots exuded POH, VAN, and SYR that may enhance the overall allelopathic potential of sorghum during growth and after harvest when residues remain on the soil surface or are incorporated prior to planting a subsquent crop.

Wheat (Triticum aestivum L.) yield is depressed when the crop is grown after grain sorghum [Sorghum bicolor (L.) Moench], known allelopathic species. Since little is known about the variability of allelopathic potential among sorghum hybrids on wheat, six sorghum hybrids were selected from a 1989–1990 sorghum‐wheat sequence for further study. The range in yield depression observed was 16%. The six hybrids were grown in 1991 and separated into plant parts at maturity. A bioassay using wheat seedlings to detect allelopathic potential was developed. Bioassays of water extracts from mature seeds, glumes, leaves, stems, and roots of sorghum were conducted to (i) quantify the allelopathic potential of sorghum on wheat; (ii) compare allelopathic potential of individual Sorghum hybrids; and (iii) identify the plant paris that are the most important sources of allelopathic substances. Wheat radicle growth response to water extracts revealed a highly allelopathic hybrid and two hybrids with low allelopathic potential. These were retained for study in 1992. All plant parts, regardless of hybrid, contained water‐soluble materials inhibitory to wheat seedling growth. Stems, leaves, and roots were the most inhibitory components of a sorghum plant, reducing wheat radicle elongation by 74.7, 68.5, 64.0%, respectively. Within a sorghum hybrid, an individual plant part was not consistently allelopathic at the same level across years. Bioassays can rapidly detect the differences in allelopathic potential that may occur within and among hybrids. These results have implications for using sorghum‐wheat rotations where residues of certain sorghum hybrids might negatively influence growth and development of wheat, possibly resulting in decreased wheat yields.

Scientists and farmers have been evaluating the intercropping of soybean [Glycine max (L.) Merr.] into wheat (Triticum aestivum L.) before harvest as an alternative to doublecropping in the lower Midwest. It was our objective to examine the interrelationships of soybean row spacing, planting date, and N applied to wheat in a wheatsoybean intercropping system. The experiment was conducted near Columbia, MO, in 1983, 1984, and 1985, on a Mexico silt loam (Udollic and Mollic Ochraqualf). Whole‐plot treatments consisted of two cropping systems (conventional and intercropped), drilled and skiprow planting patterns (0.2‐ and 0.8‐m row spacings of soybean), and three soybean planting dates coinciding with wheat growth stages. Subplots consisted of spring applied N treatments (0, 56, and 112 kg ha−1). A wheat‐soybean double crop was also included. Wheat yields were reduced 23 and 16% when soybean was intercropped in the drilled and skiprow patterns, respectively. The date of planting did not significantly (P < 0.05) influence wheat yield in the skiprow patterns. However, wheat yield was significantly (P < 0.05) decreased as planting date was delayed in the drilled pattern because of mechanical damage. Intercropped soybean yielded 27% less than conventional soybean but 28% more than doublecropped soybean over all years and treatments. Drilling soybean at the heading stage of wheat resulted in greatest yields. In 1985, N applied in excess of 56 kg ha−1 produced excessive wheat vegetative growth resulting in competition for light which caused a reduction in drilled, intercropped soybean yield. Where mechanical damage to wheat can be minimized, drilling soybean in wheat at heading can result in optimum intercrop performance.

Abstract.A thin layer chromatography (TLC) method was developed for the detection of fumonisin B 1 and B 2 in corn and corn-based feedstuffs. Finely ground samples were extracted with acetonitrile : water (1: 1), filtered, and applied to C 18 cleanup columns. The columns were washed with 1% aqueous KCl followed by acetonitrile : 1% aqueous KC1 (1:9), and the fumonisins were eluted with acetonitrile : water (7:3). The eluants were concentrated and spotted on reverse-phase C 18 TLC plates along with fumonisin B 1 and B 2 standards, and the plates were developed in methanol : 4% aqueous KCl (3:2). The fumonisins were visualized by spraying the TLC plates successively with 0.1 M sodium borate buffer, fluorescamine, and 0.01 M boric acid. The plates were then dried and examined under longwave ultraviolet light. Fumonisin B 1 and B 2 appeared as bright yellowish-green fluorescent bands at R f s of 0.5 and 0.1, respectively. The detection limit for the fumonisins on the TLC plate was 0.1 ppm in corn. Recoveries from spiked samples averaged >80%. The identification of the fumonisins was confirmed by hydrolyzing the parent compounds of B 1 and B 2 to their respective C 22 amino-alcohols and reexamining by TLC with the same visualizing reagents. This procedure was used to survey 193 corn samples collected from University of Missouri test plots in 1990 for fumonisin B,. Fumonisin B 1 was detected in 15% of the corn samples.The fumonisins, a new class of mycotoxins, have been isolated and characterized from toxic cultures of Fusarium moniloforme 1,2 and Fusarium proliferatum. 9 One of the first reports of the natural occurrence of the fumonisins described the identification of the fumonisins in corn from Transkei, Republic of South Africa. 12 Recent studies have shown fumonisin B 1 to be responsible for equine leukoencephalomalacia (ELEM) 5,6 and swine pulmonary edema. 3 In the United States, fumonisin-contaminated corn screenings have been associated with cases of ELEM 7-9,13 and swine pulmonary edema, 3,9 but only limited information is available on natural occurrence and levels of incidence of the fumonisins. A number of analytical procedures for fumonisins in corn and corn products, including thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and gas chromatography/ mass spectroscopy (GC/MS), 8,10,12,13 are available, but all are of limited value or not readily available for extensive monitoring of fumonisin contamination in corn. In this report, a rapid and sensitive TLC procedure for detecting fumonisin B 1 and B 2 in corn and corn-based feeds is described. This procedure was used to document the natural occurrence of fumonisin B 1 and B 2 in Missouri's 1990 corn harvest. Received for publication October 7, 1991. Materials and methodsSample collection. Corn samples (approximately 450 g) were collected, as part of an ongoing mycotoxin monitoring program, from the University of Missouri experimental test plots. Samples were labeled by location and hybrid. Dry land test plots were located in ...