The root-knot nematodes (RKN) (Meloidogyne graminicola) are a devastating threat to rice worldwide. The cultivated germplasm is either susceptible or moderately resistant to rice RKN. Therefore, there is a need to identify resistance sources against M. graminicola as an eco-friendly management strategy. The present study evaluated the host response of Oryza sativa genotypes comprising basmati, non-basmati improved varieties, their advanced breeding lines (83) and Oryza glaberrima accessions (42) against M. graminicola in the nematode-infested plot for two consecutive years. All O. sativa genotypes exhibited susceptible responses, while O. glaberrima accessions showed variable levels of resistance. Three of the O. glaberrima accessions (IRGC102196, IRGC102538 and IRGC102557) were highly resistant. M. graminicola significantly affected plant growth parameters in susceptible genotypes compared to resistant O. glaberrima accessions. The results were supported by histopathological studies that showed apparent giant cell formation in PR121 while penetration and development of M. graminicola juveniles were low in the O. glaberrima acc. IRGC102196. In silico analysis indicated that none of the reported nematode resistance genes from different crops had homology with the rice genome. The two anti-nematode genes (Oryzacystatin-I and Oryzacystatin-II) from O. sativa japonica revealed homology with O. sativa cv. PR121 and O. glaberrima acc. IRGC102206. Comparative analysis of these genes between PR121 and O. glaberrima acc. IRGC102206 resulted in the identification of SNPs/InDels that could be associated with nematode resistance. The identified SNPs/InDels could be validated, and further molecular studies are needed to provide insights into the resistance mechanism against rice RKN.

Following their early domestication, broomcorn millet and rice (in East Asia) and wheat and barley (in South-west Asia) were subsequently adopted across Eurasia during the Bronze Age/early historic period. The precise timing and dispersal routes for this trans-Eurasian exchange, however, remain unclear. Here, the authors present archaeobotanical evidence from sites on the Caspian Sea's southern coast, demonstrating that broomcorn millet reached West Asia by c. 2050 BC and rice by c. 120 BC. These dispersals relate to two waves of globalisation and were based on two different mechanisms: an ‘infiltration’ model (broomcorn millet) and a ‘leapfrog’ model (rice). The results contribute to our understanding of the continental-scale connectivity of the late prehistoric/early historic periods.

Water scarcity due to global warming can increase the water demand for upland rice at critical stages of crop development. However, there is little research on cultivar responses to this scenario and technologies that enhance water use efficiency (WUE). To determine the influence of water stress at and after flowering stages of drip-irrigated upland rice cultivars on physiology, yield, and WUE, a shelter experiment was conducted using a randomized block design with a split-plot arrangement of treatments. Three modern and one traditional cultivar were subjected to five irrigation managements: 100% of the field capacity considered the reference management (RM), 70 and 40% of the RM at the flowering stage, and 70 and 40% of the RM at the grain-filling stage. In general, the modern cultivars tended to maintain higher photosynthetic rate, stomatal conductance, transpiration, leaf water potential, and lower crop water stress index compared to the traditional cultivar under water stress. The WUE decreased for all cultivars under severe stress, averaging 0.55 and 0.62 kg m−3 when stress occurred at flowering and grain-filling, respectively, whereas moderate stress imposed at grain-filling maintained WUE for all cultivars, averaging 1.21 kg m−3. In addition, grain yield (GY) showed a similar variation trend under drought stress as WUE, and its reduction was mainly associated with low filled grain percentage. Among the five irrigation treatments, both GY and WUE were the highest in the RM; the best cultivar recorded 9.3 Mg ha−1 and 1.62 kg m−3, respectively. Findings suggest that attending to the full water demand under precision drip irrigation and appropriate cultivar selection can enhance upland rice production at significant levels.

Rice blast disease, caused by Magnaporthe oryzae, is one of the most damaging diseases of rice worldwide. Cultivation of rice varieties carrying resistance genes is the most economic and successful strategy to control the disease. In this study, 451 rice varieties from around the world including 363 Thai landrace rice varieties, 21 Thai improved rice varieties, 43 Japanese rice varieties and 24 worldwide rice varieties were screened by PCR technique using gene-specific markers for 10 rice blast resistance genes: Pi9, Piz-t, Pi50, Pigm(t), Pid2, Pid3, Pia, Pik, Pi54 and Pita. The results showed that 382 (99.48%) Thai rice varieties have at least one resistance gene and two rice varieties, ‘Hom’ and ‘Bak muay’, contained eight out of ten screened rice blast resistance genes. 320 rice varieties (83.33%) contained three or more rice blast resistance genes. The frequency of the rice blast resistance gene ranges from 87.76–9.64 per cent, of which the Pid3 gene has the highest frequency and the Pi54 gene has the lowest frequency. Two major resistance genes, found in Japanese rice varieties, are the Pik gene (76.74%) and the Pi9 gene (72.09%). While two major resistance genes, found in the international rice varieties are the Pi9 gene (66.67%) and the Pi54 gene (62.50%). The disease resistance gene profile of each rice variety obtained from this study will benefit the rice blast resistant breeding programme in the future.

Weedy rice (WR) (Oryza spp.) is the most troublesome weed infesting rice paddies in Brazil. Several changes have occurred in this region regarding crop management, especially WR control based on the Clearfield® (CL) rice production system launched in 2003. This survey’s objective was to evaluate the WR infestation status by assessing the producers’ perception and the management practices used in southern Brazil after 18 yr of CL use in Brazil. Rice consultants and extension agents distributed a questionnaire to 213 producers in the Rio Grande do Sul (RS) and Santa Catarina (SC) states in the 2018 to 2019 growing season. In RS, most farms are larger than 150 ha, and farmers have adopted the CL system for more than 2 yr and use minimal or conventional tillage, permanent flooding, clomazone PRE tank-mixed with glyphosate at the rice spiking stage, and crop rotation with soybean [Glycine max (L.) Merr.] or pasture. In SC, rice farms are small, averaging from 20 to 30 ha, farmers predominantly plant pre-germinated rice and do not rotate rice with other crops, and roguing is practiced. Comparing both states, the CL system is used in 99.5% and 69.3% of the total surveyed rice areas in RS and SC, respectively. Imidazolinone-resistant WR is present in 68.4% and 26.6% of rice farms in RS and SC, respectively. Rice cultivation in Brazil is currently coexisting with WR with minimal integration of control methods. However, integrated practices can control this weed and are fundamental to the sustainability of systems based on herbicide-resistant rice cultivars.

In order to understand rice blast resistance gene patterns in rice landraces from Myanmar and Laos, we analysed the Pita, Pib, Pikh, Pi9 and Pi5 genes in 80 landraces through the use of functional molecular markers and functional fragment sequencing. These landraces were separated into four haplotypes (H1–H4) based upon three mutations identified in the Pita sequence. All four haplotypes were detected among landraces from Myanmar, whereas only the H1 and H2 haplotypes were detected among landraces from Laos. We additionally grouped landraces carrying 0–4 resistance genes into 18 genotypes based upon their resistance-susceptibility patterns and found that 16 of these genotypes were detected among Myanmar landraces at relative frequencies ranging from 2.50–12.50%, while 10 were detected among landraces from Laos at relative frequencies of 2.50–42.50%. The ‘Pib( + ) pikh(−) pi9(−) pi5(−) pita(−)’ genotype was found to be dominant, accounting for 12.5 and 42.5% of landraces from Myanmar and Laos, respectively. The Pib, Pikh, Pi5 and Pita genes were detected in 52.50, 32.50, 37.50 and 30.00% of landraces from Myanmar respectively, whereas they were detected in 52.50, 12.50, 30.00 and 17.50% of landraces from Laos, respectively. The Pi9 gene was rarely detected among analysed landraces and was particularly rare in those from Laos. These findings suggest that rice landraces from Myanmar are more genetically diverse than those from Laos, with clear differences in blast resistance gene patterns between landraces from these two countries.

Tibraca limbativentris (Hemiptera: Pentatomidae) is a major pest in Neotropical rice agroecosystems. In autumn–winter, this pest takes refuge in rice stubble and in native vegetation, which allows it to re-colonize the crop during the rice growing season. However, it is still unknown whether this vegetation is a pest sink or is actually a natural trap that contributes to pest population biocontrol. Here we present information on the insect's alternative host plants, a preliminary outline of the relationship between plant phylogeny and insect abundance, and the impact that winter natural enemies have in pest population. Also, we include a proposed methodology for pest density analysis in winter hosts. Our results show significant differences in the abundance/density that T. limbativentris reaches in the 12 host plant species present in our study areas, with a plant-use pattern significantly related to the phylogenetic clade of Poales. Stink bug winter populations mainly comprised diapause adults, and 40% of insect digestive tracts had content. Survival of T. limbativentris was 56.92% in winter hosts. About mortality, 10% was due to undetermined causes and 33.08% due to entomopathogenic fungi, showing a natural regulation of the pest population. Our results suggest that native vegetation impacts winter survival of T. limbativentris. Although these plants offer shelter, they offer a greater contribution to Integrated Pest Management: the natural regulation of winter pest populations through entomopathogenic attack. Further studies on T. limbativentris population dynamics and the preservation of native areas near rice fields will be required for the development of best control practices.

The repetitive use of ALS inhibitors for smallflower umbrella sedge (Cyperus difformis L.) control has selected for herbicide-resistant (R) populations that threaten the sustainability of rice (Oryza sativa L.) production and demand alternative control measures be developed. A better understanding of seedling recruitment patterns at the field level is required to optimize the timing and efficacy of control measures. Therefore, a population-based threshold model was developed for optimizing germination prediction in multiple acetolactate synthase (ALS)-R and ALS-susceptible (ALS-S) C. difformis biotypes and applied to field-level emergence predictions. Estimated base temperatures (Tb) ranged from 16.5 to 17.6 C with no clear pattern between biotypes; such values are higher than Tb values of other important rice weeds, as well as for rice. Germination rates increased linearly from 16 to 33.7 C. ALS-R seeds germinate faster due to smaller median thermal times to germination (θT(50)) while also displaying lower germination synchronicity across water potentials. Interestingly, ALS-R biotypes were capable of germinating under lower moisture availability, as indicated by their lower (more negative) base water potential values (Ψb(50)) for seed germination; Ψb(50) values ranged from −0.24 to −1.13 MPa. In-field soil germination measurements found thermal times to emergence varied across three water regimes (daily water, flooded, or saturated). Seedling emergence under the daily water treatment was fastest; however, total seedling density was lower than for the other water regimes. In order to optimize springtime C. difformis seedling emergence, soil moisture should be kept around field capacity, as germination is hindered at lower moisture contents. By predicting when most of the seed population germinates, the thermal-time model can address issues regarding the optimal timing for herbicide applications, thereby allowing for improved C. difformis management in rice fields.

Nitrogen (N) inputs have been found to exert strong influence on leaf stoichiometry in natural ecosystems, but there are few studies investigating the effects of N in agroecosystems. Using a 5-yr fertilization experiment in rice fields, we examined the effects of N inputs on leaf stoichiometry of one crop, rice (Oryza sativa L.), and its four common weeds, barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], Monochoria korsakowii Regel and Mack, alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.], and Japanese mazus [Mazus pumilus (Burm. f.) Steenis], and further evaluated whether and how straw return mediates these effects. We found that rice and weed leaf nitrogen:phosphorus:potassium (N:P:K) stoichiometry exhibited divergent responses to N fertilizer. Weed leaf N:P:K stoichiometry was not sensitive to low (120 kg N ha−1) and regular (240 kg N ha−1) N inputs, but rice plants were, with significantly increased leaf N concentration and N:P and N:K ratios. The opposite trend was found for high N inputs (360 kg N ha−1). Rice leaf N concentration [N] did not increase further, and N:P ratios even decreased, whereas E. crus-galli and M. korsakowii had significantly increased [N] and N-related stoichiometry. We also found that the positive effects of regular N inputs on rice leaf N:P and N:K ratios were significantly dampened by straw return, but the positive effects on N:P ratios in M. pumilus leaves were enhanced by straw return. Compared with weeds, rice leaves contained low elemental concentrations across fertilization levels at grain-filling stages. These results indicate that rice has a lower N requirement than weeds at grain-filling stages, and the N supply should be managed at a relative low level to reduce the nutrient acquisition and competitive abilities of weeds. From a stoichiometric perspective, this study highlights the importance of N management in combination with straw return in controlling weeds and increasing the nutrient-use efficiency of crops.

Lying on the north-west coast of Sri Lanka, the ancient port of Mantai was ideally situated as a ‘hub’ for trade between East and West from the first millennium BC onwards. Excavations at the site were interrupted by civil war in 1984, delaying publication of these results and leading to the underestimation of Mantai's importance in the development of Early Historic Indian Ocean trade. Renewed excavations in 2009–2010 yielded extensive archaeobotanical remains, which, alongside an improved understanding of the site's chronology, provide important new insights into the development of local and regional trade routes and direct evidence for early trade in the valuable spices upon which later empires were founded.

Nicosulfuron (50 and 100 g ai ha−1), primisulfuron (40 and 80 g ai ha−1), imazethapyr (70 and 140 g ai ha-1), and DPX-PE350 (100 and 200 g ai ha-1) injury to corn, cotton, grain sorghum, rice, and soybean was evaluated at Fayetteville, AR, during 1989-90 and 1990-91. The crops were planted 0, 1, 2, 4, 8, 14 or 16, and 52 wk after herbicide application. Visible injury to all crops declined as the time interval increased. No visible injury was observed to any crop planted at least 14 wk after nicosulfuron or primisulfuron application, or 52 wk after DPX-PE350 application. Imazethapyr injured all crops except soybean at the 52-wk interval in 1990 but not in 1989.

Four-year cropping sequences of continuous cotton, cotton-soybeans-soybeans-cotton, continuous soybeans, soybeans-grain sorghum-soybeans-grain sorghum, and cotton-rice-cotton-rice were treated each year with high and low levels of herbicides to control johnsongrass. High levels of herbicide were necessary to control johnsongrass in continuous cotton, cotton-soybeans-soybeans-cotton, continuous soybeans, and the soybeans-grain sorghum rotation. Johnsongrass was not eradicated, however, after 4 years of cropping sequences with high herbicide inputs. Both low and high levels of herbicide coupled with water management required for rice production controlled johnsongrass and prevented rice yield reductions.

Growth chamber and laboratory experiments evaluated the effects of seed-soil microsite characteristics on seed germination. When corn (Zea mays L. ‘Pioneer 3541’), soybean [Glycine max (L.) Merr. ‘Corsoy 79’], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and giant foxtail (Setaria faberi Herrm. ♯ SETFA) were seeded among soil aggregates 2.50 to 1.25 cm in diameter in the growth chamber, there was decreased seedling emergence with decreasing frequency of irrigation. These same species seeded inside artificial soil aggregates showed increased seedling emergence with decreasing frequency of irrigation. The germination of corn and soybean seed inside 0.4-g, fully moist soil aggregates incubated in the laboratory under high relative humidity conditions was significantly decreased relative to seed incubated in the absence of soil. Velvetleaf and giant foxtail germination was significantly reduced by 0.1-g soil aggregates. Rice (Oryza sativa L.) had 68% emergence from 1.0-g, fully moist soil aggregates, whereas larger seeded corn and soybean had only 20 and 10% emergence, respectively. Germination inhibition of giant foxtail seed by fully moist soil was partially reversed by incubating seed-containing aggregates in an atmosphere of 75% oxygen.

Patterns of weed emergence in upland and lowland soils were observed for several months after tillage by counting all emerged species. Forty to 50% of weed emergence occurred within 6 weeks of tillage on both sites. Significant emergence occurred within 3 weeks on both sites, but very little emergence occurred within 1 week in lowland soil. The data confirm the strong influence of soil tillage on weed emergence. They also suggest an influence of radiant energy on weed emergence. Peaks of weed emergence 6 or more weeks after tillage often occurred coincident with or soon after peaks of radiant energy.

The effects of the imidazolinone herbicide AC 263,222 on crops that may be rotated with soybean were studied in the greenhouse and field. Corn, grain sorghum, cotton, rice, wheat, soybean, and Italian ryegrass were planted directly into treated soil after AC 263,222 was incorporated. In the field, AC 263,222 at rates as high as 35 g ai ha–1 did not reduce shoot weight or emergence of these species. Some visual injury occurred, but was 20% or less 28 d after planting for all crops. Crops were more sensitive in the greenhouse, where reductions in both shoot and root dry weight were observed. AC 263,222 at 13, 13, and 7 g ha–1 reduced corn, grain sorghum, and Italian ryegrass shoot weights, respectively. Cotton, rice, and wheat tolerated rates from 27 to 55 g ha–1. Biomass reduction occurred with all crops at 55 g ha–1 and above. Because AC 263,222 will be registered for use in soybean at 9 to 18 g ha–1, and potential rotational crops were planted immediately after soil treatment, problems with injury to these crops are not expected.

A field study was conducted for 3 yr to evaluate residual levels of fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) for their effects on injury and yields of rice (Oryza sativa L.). All three herbicides consistently injured rice and reduced yield at application rates above 0.1 kg/ha. These herbicides were similar in their effects on rice, but trifluralin was slightly more phytotoxic than fluchloralin or profluralin. Bioassay showed fluchloralin and trifluralin to be more inhibitory than profluralin of root and shoot elongation. The order of toxicity of the vapors of these herbicides arising from treated soil was found to be trifluralin > profluralin > fluchloralin. Grain sorghum (Sorghum bicolor L. Moench) was slightly more sensitive to these herbicides than was rice when seedlings were grown in treated soil and over 10 times more susceptible than rice to injury from their vapors. Both plant species were less affected by the herbicides in silty clay than in silt loam soil.

Field studies were conducted in 1987, 1988, and 1989 to evaluate the effects of freshly applied residual levels (simulated residue carryover) of imazaquin and norflurazon on the growth and yield of corn, cotton, grain sorghum, rice, and wheat. Studies ware conducted on five soils, and concentrations of herbicides were determined at crop planting. Crop injury ratings were recorded 4 wk after emergence, and yields were measured at the end of each growing season. In simulated residue carryover studies, corn and grain sorghum injury occurred and yields were reduced when norflurazon concentrations were 450 ng g-1 soil or greater. Rice yields were reduced at norflurazon concentrations of 710 ng g-1. Corn, cotton, and wheat heights and yields were reduced when imazaquin concentrations were 13 ng g-1, 13 ng g-1, and 45 ng g-1 soil, respectively for crops. Comparisons between simulated carryover and actual carryover were made for corn and cotton grown in imazaquin treated fields as well as for corn grown in a norflurazon treated field.

Multiherbicide granules were formulated containing 1.3% fluazifop {(±)-butyl 2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoate} (w/w) in polymerized tung oil overlaid on a granular matrix of gum xanthan-loess containing 2.7% linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide). Under greenhouse conditions the granules were as effective in selective control of velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH), hemp sesbania [Sesbania exaltata (Raf.) Cory ♯ SEBEX], corn (Zea mays L. ♯ ZEAMX), and red rice (Oryza sativa L. ♯ ORYSA) in soybeans [Glycine max (L.) Merr. ‘Hill’] as when the herbicides were sprayed separately. When applied preemergence at 0.56 to 0.14 kg ai/ha, tung oil-encapsulated fluazifop on loess granules killed 100% of stolon bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA] and was as effective as sprayed fluazifop.

The effect of adding a spray adjuvant to SAN 582H tank mixtures with fluazifop-P, imazethapyr, and sethoxydim was evaluated. SAN 582H synergistically increased broadleaf signalgrass control with reduced rates of all three postemergence (POST) herbicides when no spray adjuvant was used and when crop oil concentrate was added. For example, broadleaf signalgrass control increased from 50% to 83% when SAN 582H was tank-mixed with 52 g ai/ha sethoxydim and crop oil concentrate. In another experiment, several formulations of SAN 582H, including blank solvent-only formulations (no SAN 582H), were evaluated in combination with a reduced rate of sethoxydim to determine the source of synergism from tank mixtures. The SAN 582H molecule, not the carrier solvents in formulated product, was determined to be the source of synergism. The synergistic properties of SAN 582H were compared to other chloroacetamides. Synergism from acetochlor was similar to SAN 582H when applied POST with a reduced rate of either fluazifop-P, imazethapyr, or sethoxydim for grass control. Metolachlor also synergistically increased the control of grasses with the POST herbicides; however, metolachlor caused considerable phytotoxicity when applied alone and synergistic interactions were detected less frequently. The efficacy of sethoxydim mixed with SAN 582H was evaluated under different soil moisture conditions. Broadleaf signalgrass control increased from 81% to 93% under dry, moisture-stressed conditions when 210 g/ha sethoxydim was tank- mixed with SAN 582H.

The first significant cases of herbicide-resistant weed populations were to the triazines in the 1970s. In the last 10 years there has been an increase in the number of weed populations that have become resistant to an array of herbicides. In some of these cases, like rigid ryegrass in Australia, a multitude of resistant biotypes has evolved with different mechanisms of resistance. If the present trend continues, the number of herbicides effective on certain weed species may diminish rapidly. To counteract this trend, industry has organized a number of intercompany working groups to specifically address the development of resistance and to implement plans to manage resistance. University and extension along with industry personnel across the world have begun educating growers on resistance management. However, this effort needs to be intensified to find new solutions for controlling weeds through the use of integrated weed management practices that incorporate new and established herbicides with cultural, mechanical, and biological control methods. The challenge is to develop cost effective, environmentally sustainable programs for weed control while maintaining the present efficiency in food and fiber production so that needs of an ever expanding human population can be met.