The Mechanisms Of The Fast Eruptive Dispersal Of Weedy Rice And Its Physiological Strong Competitiveness At Seedling Stage In Jiangsu Province

Japonica rice is the most widely grown crop in Jiangsu Province. It’s planting area and yield occupied 82.9% and 84.1% of the province, respectively. Jiangsu province is one of the major rice producing provinces in China with high yield records. Its planting area and total yield is among the highest in China,7% and 10%, respectively. In recent years, the method of rice cultivation has changed from transplanting to direct-seeding, for example, direct seeding area once has reached 1/3 of the rice growing area in Jiangsu Province. As a result, the infestation of weedy rice is has increased each year with changes in rice cultivation practices. This study focus on two aspects:1. Fast eruptive dispersal of weedy rice by anthropochory:In 2005, the first reported occurrence of weedy rice was in the middle rice growing region of Jiangsu province, two years later weedy rice infestation had spread to Yanjiang area, and in 2010-2011, the entire province was infested with weedy rice. With 31 pairs of SSR markers, we analyzed the genetic diversity index and determined the dispersal route of weedy rice in Jiangsu province, in order to resolve the spreading pattern and to test if "Founder Effect" exsit or not. In addition, formal studies had reported that weedy rice in Jiangsu province may come from cultivated rice. Cultivated rice can be divided into two categories, Cultivated Varieties and Local Varieties. To further discuss the origin of weed rice in Jiangsu province, we selected cultivated varieties, landraces, and wild rice as control samples, did cluster analyze with weedy rice. This study examined:1) using 31 pairs of co-dominant SSR markers to analyze the genetic structure of 1292 weedy rice samples (683 were used in Shao Jing’s Master thesis) from 66 sampling sites in Jiangsu province, to determine if anthropochory was responsible for the fast eruptive dispersal of weedy rice in Jiangsu province.2) Adding Jiangsu indica landraces to the control sample group, which has 11 other types of rice including wild rice, to describe the relationship that exist among weedy rice, cultivated rice including landraces, and wild rice, to futher determine the origin of weedy rice in Jiangsu province. Results indicated that the genetic diversity level in Jiangsu province is low; Mantel test result show that there is no significant relationship between the 66 weedy rice groups and the geographic distance (R2=0.004, p=0.167), which illustrated that seed dispersal was the most probable way for weedy rice to spread to different areas in Jiangsu. "Founder effect" does not exist among weedy rice populations in Jiangsu Province; the UPGMA clustering result support the suggestion that weedy rice in Jiangsu mostly belong to indica category, and have closer relationship with maintainer line of three-line indica hybrid rice、Restorer line of three-line indica hybrid rice、indica rice and hybrid rice, rather than japonica rice、Jiangsu cultivated rice、Jiangsu japonica landraces(Lu dao and Tang dao); Sructure analysis result is similar to UPGMA clustering result. This study indicated that weedy rice in Jiangsu Province possibly come from indica cultivated rice rather than indica landraces.2. The mechanisms of the competitiveness of weedy rice in the seedling stage:Field investigations show that weedy rice grows more vigorously than cultivated rice in seedling stage. Formal biological observations of weedy rice show that 45 days after sowing (DAS), plant height is higher than that of cultivated rice, but whether the difference can be seen earlier than 45 days and what the mechanisms behind this difference haven’t been reported. Green plants depend on light for growth and maturation, while photosynthesis studies on weedy rice mostly centered on reproduction stage, few on seedling stage, and no reports have been found about this primary reaction. Because of the luminous energy shift from photosynthesis activity to dissipation as heat or fluorescence, we can study chlorophyll fluorescence to seek information about plant growth and electron transport, by applying the JIP-test analyzing method.We selected weedy rice samples from 6 sites equally distributed in Jiangsu province to compare with the typical japonica rice cultivated. Daily germination rate after being sown until 7 DAS were determined. Seedling plant height and fast fluorescence parameters were measured weekly from 14 DAS till 35 DAS. Results show that all lines of weedy rice emerged 2 days earlier than the rice cultivar. No dormancy trait was found in weedy rice in Jiangsu province. In the seedling stage, weedy rice has already shown diversity and all weedy rice seedlings are taller than cultivated rice of 35 DAS. The comprehensive photosynthesis parameter, PI(abs), of weedy rice is higher than cultivated rice, indicating higher photosynthesis ability in weedy rice.