In this study, responses of rice under drought stress correlating with changes in chemical compositions were examined. Among 20 studied rice cultivars, Q8 was the most tolerant, whereas Q2 was the most susceptible to drought. Total phenols, total flavonoids, and antioxidant activities, and their accumulation in water deficit conditions were proportional to drought resistance levels of rice. In detail, total phenols and total flavonoids in Q8 (65.3 mg gallic acid equivalent (GAE) and 37.8 mg rutin equivalent (RE) were significantly higher than Q2 (33.9 mg GAE/g and 27.4 mg RE/g, respectively) in both control and drought stress groups. Similarly, the antioxidant activities including DPPH radical scavenging, β-carotene bleaching, and lipid peroxidation inhibition in Q8 were also higher than in Q2, and markedly increased in drought stress. In general, contents of individual phenolic acids in Q8 were higher than Q2, and they were significantly increased in drought stress to much greater extents than in Q2. However, p-hydroxybenzoic acid was found uniquely in Q8 cultivars. In addition, only vanillic acid was found in water deficit stress in both drought resistant and susceptible rice, suggesting that this phenolic acid, together with p-hydroxybenzoic acid, may play a key role in drought-tolerance mechanisms of rice. The use of vanillic acid and p-hyroxybenzoic acid, and their derivatives, may be useful to protect rice production against water shortage stress.

Induced point mutations are important genetic resources for their ability to create hypo- and hypermorphic alleles that are useful for understanding gene functions and breeding. However, such mutant populations have only been developed for a few temperate maize varieties, mainly B73 and W22, yet no tropical maize inbred lines have been mutagenized and made available to the public to date. We developed a novel Ethyl Methanesulfonate (EMS) induced mutation resource in maize comprising 2050 independent M2 mutant families in the elite tropical maize inbred ML10. By phenotypic screening, we showed that this population is of comparable quality with other mutagenized populations in maize. To illustrate the usefulness of this population for gene discovery, we performed rapid mapping-by-sequencing to clone a fasciated-ear mutant and identify a causal promoter deletion in ZmCLE7 (CLE7). Our mapping procedure does not require crossing to an unrelated parent, thus is suitable for mapping subtle traits and ones affected by heterosis. This first EMS population in tropical maize is expected to be very useful for the maize research community. Also, the EMS mutagenesis and rapid mapping-by-sequencing pipeline described here illustrate the power of performing forward genetics in diverse maize germplasms of choice, which can lead to novel gene discovery due to divergent genetic backgrounds.

Meristems are central to plant growth and development, yet evidence of directly manipulating this control to improve crop yield is scarce. Kernel row number (KRN) is an important agronomic trait that can directly affect maize (Zea mays L.) yield. However, this trait is difficult to select by phenotyping, since it is highly variable in the mixed genetic backgrounds in early selfing generations. This study sought to improve this trait by marker-assisted backcrossing (MABC) of a weak allele of FASCIATED EAR 2 that is known to affect inflorescence meristem size, but the effect of which on yield is unclear. All of the four introgressed tropical elite inbreds of different heterotic groups, which are homozygous for the fea2-1328 allele, had 2–5 more KRNs compared to their respective recurrent parents. Furthermore, one hybrid made from crosses between two introgressed parents also had KRN increases that resulted in up to 28% yield increase compared to the original hybrid across multiple yield trials. The novel negative effects of the pericentromeric fea2 and/or its linkage drag effect on plant height, seed weight, and ear length, which could prevent line improvement, were revealed in several genetic backgrounds. Integration of conventional phenotypic selection to overcome these undesirable effects was discussed. This is the first work to demonstrate the possibility to increase yield of maize varieties using a mutation in a meristem size regulator. The crossing, selection strategies, and recombinant lines in this work can be applied to other elite maize hybrids and provide a potentially straightforward, non-transgenic way to improve the yield of an existing variety by 8–28%.

The objective of this study was to evaluate the allelopathic responses of rice seedlings under submergence stress at different temperatures (10, 25, 32, and 37 °C). The results showed that a wide range of allelopathic responses of rice seedlings depended on varieties and stress conditions, with temperature was being a key factor. It showed that the extracts of rice seedlings induced significant suppression on lettuce and radish seedling germination, but had negligible allelopathic effects on growth of barnyardgrass, whilst the emergence and growth of natural weeds was stimulated. In contrast, the root exudates of Koshihikari rice seedlings (K32) at 32 °C reduced the number of total weeds by ≈60.0% and the total dry weight of weeds by 93.0%; i.e., to a greater extent than other root exudates. Among the 13 identified phenolic acids, p-hydroxybenzoic, vanillic, syringic, sinapic and benzoic acids—at concentrations of 0.360, 0.045, 3.052, 1.309 and 5.543 μg/mL might be involved in allelopathic responses of K32, inhibiting the growth of barnyardgrass and natural weeds. Findings of the present study may provide useful information on allelopathic responses of rice under environmental stresses and thus further understand of the competitive relationships between rice and weeds under natural conditions.

Pinto peanut (Arachis pintoi Krapov. & W.C. Greg.) is an herbaceous perennial plant which belongs to the Leguminosae family. This plant is well known for its use as a cover crop, but little information is available on the allelopathic potential of this legume. Therefore, this study aimed to explore the allelopathic effects of A. pintoi under various screening conditions and to analyze its potential allelochemicals using gas chromatography–mass spectrometry (GC-MS). In laboratory bioassays, aqueous extracts of A. pintoi powder exerted the average inhibition of the growth of Echinochloa crus-galli (55.1%), Oryza sativa (77.1%), and Vigna radiata (60.1%), respectively, of which the root lengths of the tested plants were the most suppressed. In greenhouse experiments, E. crus-galli was inhibited by 63.4% at 200 g/m² of A. pintoi dried powder application. In field trials, A. pintoi also significantly reduced the growth of E. crus-galli and natural weeds. By incorporating a dose of 200 g/m², the average inhibition of E. crus-galli was 43.9%, the dry weight of natural paddy weeds was 43.1%, and rice yield was simultaneously increased by 35%. The growth inhibitions of weeds and tested plants were proportional to the doses of A. pintoi applied and varied with the tested plant species. Among three different solvent extracts (methanol, hexane, and ethyl acetate), the hexane extract exerted the highest suppression against the growth of E. crus-galli and L. sativa by IC₅₀ against root and shoot growth = 4.08 and 8.4 mg/mL and 1.7 and 1.54 mg/mL, respectively, followed by ethyl acetate extract, while the least effective was methanol extract. From those extracts, a total of 35 substances were detected by GC-MS analyses, including 14 newly identified constituents, such as phenolic acids, stearic acid, palmitic acid, fatty acids, pyranones, and benzofurans, which may be responsible for the herbicidal effects of A. pintoi. This study suggests that A. pintoi may be used as a source of bioherbicide to minimize the dependency on harmful synthetic herbicides and enhance rice yield.

Volume 56: Weed Allelochemicals and Possibility for Pest Management