Bitter gourd (Momordica charantia L.) is a commercially and nutritionally important market vegetable in Asia cultivated mainly by smallholder farmers. Cucurbit powdery mildew (CPM) caused by Podosphaera xanthii (Px) is a nearly ubiquitous and serious fungal disease of bitter gourd. Five bitter gourd breeding lines (THMC 113, THMC 143, THMC 153, THMC 167, and THMC 170) were selected at the World Vegetable Center for resistance to a local isolate of Px in Kamphaeng Saen, Thailand. We evaluated the resistance potential of these five inbred lines against local isolates of Px at 12 locations in five Asian countries. Plants were inoculated with the respective local Px isolate 15 and 30 days after transplanting and additional Px-infected plants of the inoculated control were interplanted throughout each test. Plants were rated 60 days after transplanting for CPM reaction using a 0 (no evidence of infection) to 5 (>75% infection evident on individual leaves) disease severity scale. THMC 153 and THMC 167 were resistant to the local race of Px in all locations, whereas THMC 143 was observed resistant in all test locations except one in China. THMC 113 was resistant in each location except one in India. THMC 170 was susceptible in three locations in India. The multilocation tests revealed four unique Px races on bitter gourd in different Asian countries and sources of resistance for breeding CPM-resistant bitter gourd cultivars. Six strains of Px isolated from other cucurbits (Cucumis and Cucurbita) and representing five melon CPM races were unable to infect the susceptible M. charantia accession THMC 144 and the five resistant breeding lines, indicating pathotype differences between them and an isolate of M. charantia origin typed as race 1 on melon. THMC 143 and THMC 167, which originated from India, exhibited good yield potential in trials conducted in Thailand, Myanmar, Vietnam, and Bangladesh.

BACKGROUND Beckmannia syzigachne (Steud.) Fernald has become a dominant weed that has evolved resistance to major herbicides used in the wheat fields of rice‐wheat double cropping areas of the middle and lower reaches of the Yangtze River, China. Seed dispersal occurs over long distances via irrigation water. As mechanical harvesting services popularize, there is concern that combine harvesters could play an increasing role in B. syzigachne seed dispersal. RESULTS Random sampling of 30 combine harvesters at wheat harvest determined that an average of 8000 B. syzigachne seeds remain in the combine after wheat harvesting, predominantly on the metal plate. These seeds could potentially be transported into adjacent fields. A double exponential model predicted that seeds remaining on the metal plate could be dispersed over 7885 m2 into the next field. Within a field, the number of fallen seeds and their dispersal distance were positively correlated to panicle density. Combines spread seeds away from the source potentially creating new weed patches. During irrigation and rotary tillage ploughing, 70% of B. syzigachne seeds scattered in the field floated on the water surface and were moved away by the wind. CONCLUSION Both wheat combine harvesters and water flow effectively spread B. syzigachne seeds. Areas with high B. syzigachne population density should be carefully harvested separately, and the metal plate should be carefully cleaned to prevent spreading the weed across fields and region. Floating B. syzigachne seeds displaced to field edges by water can be physically removed with nets to prevent further distribution by water.

BACKGROUND: Beckmannia syzigachne (Steud.) Fernald has evolved herbicide resistance due to the long-term sole use of herbicides and has become a dominant weed in wheat fields in the middle and lower reaches of the Yangtze River in China. In addition to the selection pressure imposed by herbicides, pollen-mediated gene flow (PMGF) has been reported to cause the spread of herbicide resistance between populations within a certain range in some farmland weeds. It is not clear whether the same is true for the self-pollinated grass weed B. syzigachne. RESULTS:In this study, we confirmed and quantified the level of PMGF in B. syzigachne through concentric circle planting and herbicide resistance tests. Results show that when the B. syzigachne pollen donor was close to the recipient (0.5 m), the average gene flow was 0.66%. Gene flow was detected as far as 10 m (the farthest distance studied) and decreased exponentially with increasing distance, which could be described by a double exponential decay model. Temperature also affected gene flow, whilst the average level of gene flow in all directions of wind was similar and wind speed caused insignificant difference in gene flow. CONCLUSION:The results of this study confirmed that PMGF can occur between B. syzigachne populations in adjacent fields. Although the level of resistance spreading by pollen was low, especially across long distance, the results were relevant for smallholding farms, which is the dominant form of agricultural operation in China. It is therefore important to take proactive measures and integrate chemical and ecological weed control methods to prevent the spread of resistant B. syzigachne via both seeds and pollens.