Research and Development in Tropical Agriculture, SA
Recent Published Articles
Cytoplasmic-genetic male sterility gene provides direct evidence for some hybrid rice recently evolving into weedy rice
May 31 2015
Zhang JX, Lu Z, Dai WM, Song XL, Peng Y, Valverde BE, Qiang S
Weedy rice infests paddy fields worldwide at an alarmingly increasing rate. There is substantial evidence indicating that many weedy rice forms originated from or are closely related to cultivated rice. There is suspicion that the outbreak of weedy rice in China may be related to widely grown hybrid rice due to its heterosis and the diversity of its progeny, but this notion remains unsupported by direct evidence. We screened weedy rice accessions by both genetic and molecular marker tests for the cytoplasmic male sterility (CMS) genes (Wild abortive, WA, and Boro type, BT) most widely used in the production of indica and japonica three-line hybrid rice as a diagnostic trait of direct parenthood. Sixteen weedy rice accessions of the 358 tested (4.5%) contained the CMS-WA gene; none contained the CMS-BT gene. These 16 accessions represent weedy rices recently evolved from maternal hybrid rice derivatives, given the primarily maternal inheritance of this trait. Our results provide key direct evidence that hybrid rice can be involved in the evolution of some weedy rice accessions, but is not a primary factor in the recent outbreak of weedy rice in China.
(A) Hybrid rice breeding field, (B) Artificial hybridization of rice plants; (C) Self-crossing of rice individuals,
(D) Morphology of some weedy rice accessions. Photographs provided by Jingxu Zhang, Nanjing Agricultural
Scientific Reports 5:10591. Doi:10.1038/srep10591
Download a free reprint at http://www.nature.com/srep/2015/150527/srep10591/full/srep10591.html
ICE1 demethylation drives the range expansion of a plant invader through cold tolerance divergence
April 10 2015
Xie HJ, Li H, Liu D, Dai WM, He JY, Lin S, Duan H, Liu LL, Chen SG, Song XL, Valverde BE, and Qiang S.
Cold tolerance adaption is a crucial determinant for the establishment and expansion of invasive alien plants into new cold environments; however, its evolutionary mechanism is poorly understood. Crofton weed (Ageratina adenophora), a highly invasive alien plant, is continuously spreading across subtropical areas in China, north-eastward from the first colonized south-western tropical regions, through cold tolerance evolution. Close relations between the cold tolerance levels of 34 populations, represented by 147 accessions, and the latitude, extreme lowest temperature, coldest month average temperature, and invasion period have provided direct insight into its cold tolerance divergence. A comparative study of the CBF pathway, associated with the cold tolerance enhancement of cold-susceptible CBF1-transgenic plant, among four geographically distinct crofton weed populations revealed that the CBF pathway plays a key role in the observed cold tolerance divergence. Four epialleles of the cold response regulator ICE1 ranged from 66 to 50 methylated cytosines, representing a 4.4% to 3.3% methylation rate and significantly corresponding to the lowest to highest cold tolerance levels among these different populations. The significant negative relation between the transcription levels of the primary CBF pathway members, except for CBF2, and the methylation levels among the four populations firstly demonstrates that the demethylation-upregulated transcription level of CBF pathway is responsible for this evolution. These facts, combined with the cold tolerance variation and methylation found among three native and two other introduced populations, indicate that the ICE1-demethylated upregulation of cold tolerance may be the underlying evolutionary mechanism allowing crofton weed to expand northward in China.
Molecular Ecology 24:835-850. 2015.
Glyphosate spray drift in Coffea arabica – Sensitivity of coffee plants and possible use of shikimic acid as a biomarker for glyphosate exposure.
August 20 2014
Lars C. Schrübbers, Bernal E. Valverde, Jens C. Sørensen and Nina Cedergreen
Glyphosate is widely used in coffee plantations to control weeds. Lacking selectivity, glyphosate spray drift is suspected to cause adverse effects in coffee plants. Symptoms caused by glyphosate can be similar to those produced by other stress factors. However, shikimic acid accumulation should be a useful biomarker for glyphosate exposure as shown for other crops. The aim of this study was to assess the sensitivity of coffee plants towards glyphosate on different biological response variables and to evaluate the use of shikimic acid as biomarker. Dose–response experiments yielded ED50 values (50% effect dose) in the range of 38–550 g a.e. ha-1 depending on the quantitative or qualitative variable monitored. The frequency of plants showing symptoms was the most sensitive variable. The best sampling time for shikimic acid accumulation was 1-2 weeks after glyphosate application, depending on experimental conditions. The highest shikimic acid accumulation was observed in young leaves. Shikimic acid is a suitable biomarker for a glyphosate exposure in coffee, using only young leaves for the analysis. Young coffee plants are susceptible to glyphosate damage. If symptoms are absent the risk of severe crop damage or yield loss is low.
Pesticide Biochemistry and Physiology 115:15–22. 2014.
Cyperus difformis evolves resistance to propanil
May 4 2014
Bernal E. Valverde, Louis G. Boddy, Rafael M. Pedroso, James W. Eckert, Albert J. Fischer
Cyperus difformis L. is one of the worst weeds of rice world-wide and has evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in rice fields of California. Propanil use was intensified to control the widespread resistant biotypes. Rice growers have recently experienced poor control, suggesting resistance to this photosystem II-inhibiting herbicide may have evolved in C. difformis populations. The objectives of this study were to detect the presence of propanil resistance, to establish resistance levels, and to investigate involvement of enhanced herbicide detoxification as mechanism of resistance through the use of metabolic inhibitors. Four C. difformis populations collected in rice fields from the Sacramento Valley of California were confirmed resistant to propanil. This is the first case of such resistance outside the Poaceaeand the first time C. difformis exhibits resistance to an herbicide mechanism of action other than ALS inhibition. Carbaryl and malathion applied individually in mixture with propanil had minor effects on herbicide toxicity suggesting metabolic detoxification was not a resistance mechanism. A resistant biotype produced more than 80% biomass after a propanil (6.7 kg a.i. ha−1) and carbaryl (1.9 kg a.i. ha−1) or propanil and malathion (1.0 kg a.i. ha−1) treatment compared to <20% by a susceptible biotype, suggesting substantial resistance still persisted in spite of insecticide addition. Propanil-resistant plants were cross-resistant to bensulfuron-methyl, imazosulfuron, halosulfuron-methyl and penoxsulam, but susceptible to carfentrazone. The loss of propanil to control this important weed of rice underscores the fragility of herbicide-based weed control in monoculture rice. Integrated weed management approaches to decrease herbicide selection pressure are needed to mitigate the evolution of multiple-herbicide resistance in C. difformis of California rice.
Photograph of resistant and susceptible plants and dose response graph kindly provided by Dr. Rafael M. Pedroso.
Photograph of C. difformis in rice field by J. DiTomaso (UC Davis).
Crop Protection 62:16–22. 2014.