Genetic Diversity and Relationship of Weedy Rice in Taizhou City, Jiangsu Province, China

Microsatellite markers and morphological characteristics were used to explore the genetic diversity and possible origin of weedy rice in Taizhou City, Jiangsu Province, China. Fifty-two weedy rice (Oryza sativa L.) accessions were compared with two wild rice, four hybrid rice and five cultivars using 22 simple sequence repeat (SSR) primer pairs. A total of 107 fragments were amplified, averaging 5.6 alleles per primer pair. The polymorphic index content (PIC) values ranged from 0.3077 to 0.7951, averaging at 0.5870. The average genetic distance of all samples ranged from 0.02 to 0.46 with an average of 0.262. The genetic distance among Taizhou weedy rice ranged from 0.03 to 0.44 with an average of 0.224. Cluster analysis showed that all the weedy rice accessions from Taizhou City were indica, and could be subdivided into different genotypes. The majority (86%) of weedy rice was most closely related to hybrid rice. The Taizhou weedy rice accessions were morphologically similar, but still could be delineated into indica or japonica group by some morphological traits. It is suggested that the levels of genetic and morphological diversities of weedy rice in Taizhou City are low and these weedy rice plants originated from the segregating progenies of hybrid rice that had naturally introgressed with cultivated rice.

Morphological and Physiological Responses of Weedy Red Rice (<i>Oryza sativa</i>L.) and Cultivated Rice (<i>O. sativa</i>) to N Supply

Red rice (Oryza sativa L.), a noxious weed in rice production, competes with cultivated rice for nutrients. Accumulation of more N in red rice than in cultivated rice may be due to a mechanism different from that of cultivated rice. To test this assumption, red rice and cultivated rice were grown in nutrient solution to compare their growth and physiological responses to N supply. Experimental design was a split-plot, where main plot factor was rice type (Stf-3, ‘Wells’);split-plot factor was N treatment [T1 (complete nutrient solution);T2 (–NH4NO3);T3 (+NH4NO3 for 24-h post-N deficiency);and T4 (+NH4NO3 for 48-h post-N deficiency)]. Nitrogen deficiency was defined as N sufficiency index (NSI) 4, Stf-3 showed higher increment in root length and surface area than Wells. Shoot tissue concentrations of N and total sugars were measured to determine physiological response in N-deficient and N-supplemented plants. Stf-3 had greater N and sucrose tissue concentrations at N-deficient conditions compared with Wells, implying a stress-adaptive molecular mechanism regulated by N and sucrose availability.

A Survey of Genetic Diversity of the Weedy Species <i>Ipomoea lacunosa</i>L. in the USA Mid-South

Morningglories (Ipomoea spp.) are among the most troublesome weedy species in agroecological environments. Ipomoea lacunosa is one of the most prevalent of these species. Localized adaptations resulted in the evolution of several I. lacunosa ecotypes in North America, which could potentially impact its response to crop management practices. To evaluate the genetic diversity and population structure of I. lacunosa populations, we amplified inter-simple sequence repeats loci by polymerase chain reaction (ISSR-PCR) of 64 accessions using 14 ISSR primers for Ipomoea. Of these, 64 polymorphic fragments were scored. Analysis of Nei’s genetic distance (GD) values placed the accessions into four genotypic clusters, two of which were composed primarily of accessions from Arkansas and Mississippi with GD between clusters of 0.318. The overall GD was 0.238, indicating a narrow genetic base. Population structure analysis determined three ancestral subgroups, with the majority of Arkansas and Mississippi accessions separated into two subgroups. The existence of various genotypes and ecotypes of I. lacunosa demonstrates the evolutionary diversification of this weedy species as it adapts to new colonized environments and agricultural activities.