Dynamic Development of Aphelenchoides besseyi on Rice Plant by Artificial Inoculation in the Greenhouse

A study was done on the relationship between Aphelenchoides besseyi and the symptoms of small grains and erect panicles. This is an important rice disease in Jiangsu Province, China. A. besseyi was extracted from small grains and erect panicles and cultured artificially, and then inoculated into bud and leaf sheaths of seedlings of two Oryza sativa cultivars, namely Zhendao 2 and Wuyunjing 7 in a greenhouse. The effect on rice growth, in particular the small grains and erect panicles, was revealed by the extent of the disease, seed expansion stages, nematode load, and nematode mortality. In contrast to healthy seedlings, the height, length, and the numbers of spikelets of unhealthy panicles of Zhendao 2 were decreased by 6.7, 16.4, and 13.5%, respectively. Before anthesis, nematodes were attracted to the leaf sheath and apical meristem, nematode load increased by 40%; after anthesis, nematodes occurred in spikelets principally and the number increased by 90.8%. The percentages of infected seeds and nematode load were highest in plump seeds and lowest in empty seeds. Nematode mortality on grain with normal endosperm was lower than seeds with abnormal endosperm. Results indicated that A. besseyi was the pathogen in rice with the symptoms of small grains and erect panicles. Wuyunjing 7 manifests only the small grains and erect panicles symptoms and not the symptoms of leaf white-tip. These symptoms of small grains and erect panicles are new symptom records for the disease caused by A. besseyi on rice.     

Natural Variation of Leaf Thickness and Its Association to Yield Traits in indica Rice

Leaf thickness is an important morphological trait in rice. Its association to the yield potential, as of now has not been documented because of the shortage of the equipment which could conveniently measure the leaf thickness in rice. In this study, the thickness of top three leaves of 208 cultivars had been determined by a nondestructive rice leaf thickness instrument for the research of the natural variation of leaves thickness and its association to yield traits in indica rice. The results showed that the flag leaf was the thickest, and the 2nd leaf was thicker than the 3rd leaf. Analysis of variance indicated the existence of wide genetic diversity of leaf thickness among the investigated indica rice genotypes. The tight correlation among the thicknesses of the top three leaves means that the leaf thickness traits share one genetic control system. Leaf thickness had a significant positive correlation with leaf length and a positive correlation with leaf width, indicated that thicker leaf was beneficial to increasing the single leaf area. The results of correlation analysis revealed that thicker leaf should be profitable to the leaf erection, higher numbers of grains per panicle and higher grains weight per panicle. However, the significantly negative correlation between leaf thickness and number of panicles per plant counteracted the profitability from increased grains weight per panicle, so that the correlations of the thicknesses of the top three leaves to yield and biomass were positive but not significantly. It has made great progress in the genetic improvement of leaves thickness in inbred indica rice breeding in Guangdong Province, China, since the 1990s.     

Yield characteristics of japonica/indica hybrids rice in the middle and lower reaches of the Yangtze River in China

Although a lot of researches have been done on yield characteristics of japonica/indica hybrid rice, there is little information on differences of yield characteristics between different types of hybrid. To determine common characteristics of japonica/indica hybrid rice(JIHR) and identify the differences between different types of JIHR, the present study assessed yield characteristics, such as panicle trait, leaf area index(LAI), above-ground biomass accumulation, and nitrogen absorption and utilization, among three types of cultivar of JIHR. In our field experiments, three types of JIHR, e.g., Yongyou, Chunyou and Jiayouzhongke, were divided, and each of them has two cultivars, which were used as materials, meanwhile, using conventional japonica rice(CJR) Wuyingjing 31 and Sujing 9 were as controls. The results showed that the mean yield of those JIHR was above 12 t ha–1 in 2017 and 2018, and was 31.9 and 32.2%, respectively higher than that of CJR in the two years. Spikelet number per panicle of JIHR resulted in high yield. Higher yield of JIHR was likely contributed to greater panicle number and more spikelets per panicle. Higher yielding JIHR showed stronger tillering capacity, larger LAI and above-ground biomass accumulation from jointing to heading stages, which likely contributed to the higher number of spikelets per panicle. The long duration from heading to maturity stages allowed more nitrogen accumulation of higher yielding JIHR.     

Comparative analysis on grain quality and yield of different panicle weight indica-japonica hybrid rice(Oryza sativa L.) cultivars

Indica-japonica hybrid rice(Oryza sativa L.) cultivars showed high yield potential and poor tasting quality when compared with common japonica rice cultivars. Large panicle is a prominent factor of high yield for indica-japonica hybrid rice cultivars, and the panicle weight varies greatly among different indica-japonica hybrid rice cultivars. It is important to research on yield and grain quality of different panicle weight indica-japonica hybrid rice cultivars. In this study, two different panicle types indica-japonica hybrid cultivars were used to research on the relation of yield and grain quality. The yields of two heavy panicle weights indica-japonica hybrid cultivars were significantly higher than that of two medium panicle weight rice cultivars. The cooking and eating quality and starch properties of different panicle type cultivars were evaluated. Yongyou 6715(medium panicle) and Yongyou 1852(heavy panicle) got the relatively higher cooking and eating quality. Rice cultivars with medium panicle weight had more large starch granules and higher relative crystallinity than cultivars with heavy panicle weight. Transition temperature and retrogradation enthalpy(ΔHret) of medium panicle type cultivars were significantly higher than that of heavy panicle type cultivars. There was no significant difference in amylose content among different panicle type cultivars. Protein content of heavy panicle type cultivar was higher than that of medium panicle type cultivar, and protein content is the main factor affect cooking and eating quality in this study. The cultivar Yongyou 6715 got the highest taste value with the lowest protein content. Thus, it is suggested that the emphasis on improving rice cooking and eating quality of indica-japonica hybrid rice cultivars is how to reduce the protein content in rice grain. According to the results of this study, medium panicle type with high grain weight is the desired panicle type for high quality indica-japonica hybrid rice breeding.     

Higher leaf area through leaf width and lower leaf angle were the primary morphological traits for yield advantage of japonica/indica hybrids

The yield potential of japonica/indica hybrids (JIH) has been achieved over 13.5 t ha⁻¹ in large-scale rice fields, and some physiological traits for yield advantage of JIH over japonica inbred rice (JI) and indica hybrid rice (IH) were also identified. To date, little attention has been paid to morphological traits for yield advantage of JIH over JI and IH. For this reason, three JIH, three JI, and three IH were field-grown at East China (Ningbo, Zhejiang Province) in 2015 and 2016. Compared with JI and IH, JIH had 14.3 and 20.8% higher grain yield, respectively, attributed to its more spikelets per panicle and relatively high percentage of filled grains. The advantage in spikelets per panicle of JIH over JI and IH was shown in number of grains on the upper, middle, and lower branches. Compared with JI and IH, JIH had higher leaf area through leaf width and lower leaf angle of upper three leaves, higher leaf area index and leaf area per tiller at heading and maturity stages, higher stem weight per tiller and K and Si concentrations of stem at maturity, higher dry matter weight in leaf, stem, and panicle at heading and maturity stages, and higher biomass accumulation after heading and lower biomass translocation from stem during ripening. Leaf width of upper three leaves were correlated positively, while leaf angle of upper three leaves were correlated negatively with biomass accumulation after heading, stem weight per tiller, and per unit length. Our results indicated that the grain yield advantage of JIH was ascribed mainly to the more spikelets per panicle and relatively high percentage of filled grains. Higher leaf area through leaf width and more erect leaves were associated with improved biomass accumulation and stem weighing during ripening, and were the primary morphological traits underlying higher grain yield of JIH.     

Comparison of grain yield and quality of different types of japonica rice cultivars in the northern Jiangsu plain,China

In recent years, an increasing number of different types of japonica rice cultivars have been released in the southern rice region of China. The grain yield and quality of these new cultivars showed significant differences in large scale planting. However, the causes of the differences remain little known. Therefore, three typical types of japonica rice cultivars were used in this study to investigate their grain yield and quality. A scanning calorimeter(DSC), X-ray powder diffractometer(XRD), rapid viscosity analyzer(RVA) and taste analyzer were used to evaluate the cooking and eating properties. The results showed that the yield of non-soft hybrid japonica rice cultivars was significantly higher than that of non-soft inbred japonica rice cultivars and soft inbred japonica rice cultivars. Soft inbred japonica rice cultivars had a low amylose content and moderate protein content, which are the main reasons for the superior cooking and eating quality. In addition, the relative crystallinity of soft inbred japonica rice cultivars was significantly higher than that of non-soft inbred and non-soft hybrid japonica rice cultivars, which is considered the major factor resulting in higher transition temperature and gelatinization enthalpy(ΔHgel). Non-soft hybrid japonica rice cultivars had a higher number of large starch granules than soft inbred and non-soft inbred japonica rice cultivars. The setback value(SB) and breakdown value(BD), indirectly reflecting the cooking and eating quality of the three types of japonica rice cultivars, also confirmed that soft inbred japonica rice cultivars with a low SB value and a high BD value had better palatability than the other two types. This study provides guidance for future plantation of different types of japonica rice cultivars in large rice-producing areas.     

The breeding of japonica rice in northern China: An 11-year study(2006–2016)

The world's population is facing food shortages due to climate change and the competition for arable land between food and energy crops. Many national and international projects to develop "super rice" cultivars were established in recent decades to attain a ‘third leap forward' in rice production. In order to evaluate the breeding process in northern China, an 11-year tracking survey of japonica rice breeding, which involved a total of 520 rice accessions and 67 test plots, was completed in this study. The results showed that the yields of these accessions had increased stably, which was similar to control check varieties(CKs). The breeding strategy reduced the panicle number and increased the grain number per panicle through an increase of spikelet density(number of grains per centimeter on the panicle). This high spikelet density benefits not only the yield but also the blast resistance and amylose content. At higher latitudes, the preferred rice accessions had slim grain shape and extended growth period. In the middle latitudes among the test plots, the breeders focused on reducing the amylose content to improve the cooking quality of the rice accessions. Yield and blast resistance were the two highest priorities during the breeding selection process. The present study evaluated the breeding process in northern China during the last decade, which may lead to new insights into the future of rice breeding.     

Effect of ecological environments on subspecies characteristics and economic traits in filial generations of cross between indica and japonica rice

Two recombinant inbred lines (RILs) populations, RILSA derived from the cross between “Zhongyouzao8” (indica) and “Toyonihiki” (japonica) rice cultivars, and RILSB derived from the cross between “Qishanzhan” (indica) and “Akihikari” (japonica) rice cultivars, were grown in Liaoning and Sichuan Provinces, China to understand the effects of ecological environments on the subspecies characteristics and economic traits in filial generations of cross between indica and japonica. The results showed that both the subspecies characteristics and economic traits changed significantly. The effects of ecological environments on Cheng’s index and six subspecies characteristics were different on the basis of populations or characteristics. The distribution of Cheng’s index in RILSA was japonicalinous in Liaoning and Sichuan. The distribution of Cheng’s index in RILSB approached to normal distribution in Liaoning, but it was japonicalinous in Sichuan. As a whole, the two populations were more japonicalious in Sichuan than in Liaoning. The panicle number, seed setting rate and per-thousand-grain weight were decreased significantly in Sichuan. The grain number per panicle showed no significant change. A significant positive correlation was found between Cheng’s index and the economic traits, including six subspecies traits. It suggested that the reason that the filial generation of cross between indica and japonica in northern China showed japonicanous subspecies characteristics might be the artificial selection by breeders on the economic traits. In addition, indica-japonica differentiation and the relationship with ecological environments were discussed. __________ Translated from Progress in Natural Science, 2007, 17(8): 42–47 [译自: 自然科学进展]     

Analysis of Variations in White-Belly and White-Core Rice Kernels Within a Panicle and the Effect of Panicle Type

This study aims to investigate the variation in occurrence of white-belly rice kernel（WBRK） and white-core rice kernel（WCRK） among different positions within a panicle. Twenty-four M4 mutants involved in four panicle types, namely the compact, intermediate, loose, and chicken foot panicle were used. They derived from a japonica rice cultivar Wuyujing 3. Considerable differences in morphological characters existed among the four types of panicle, especially in panicle length, the secondary branch number and ratio of grain number to total branch length. Marked differences were found in WBRK and WCRK among different positions within a panicle for all types of panicle. In general, grains located on the primary rachis and top rachis branches had higher WBRK and WCRK percentage than those on the secondary rachis and bottom rachis branches. WCRK exhibited larger variation among grain positions than WBRK did. Moreover, there was a significant difference in WCRK/WBRK among grain positions within a panicle, with primary rachis and top rachis branches having higher values than the secondary and bottom rachis. In addition, panicle type showed no significant effect on the pattern of WBRK and WCRK occurrence within a panicle. The results indicated the difference in mechanism of WBRK and WCRK formation in grain position within a panicle, and are valuable for breeding and agronomic practices aimed at lowering chalky grain rate.     

Geographic variation in the yield formation of single-season high-yielding hybrid rice in southern China

Environmental conditions greatly affect the growth of rice. To investigate the geographic differences in yield formation of single-season high-yielding hybrid rice in southern China, experiments were conducted in 2017 and 2018 in the upper and middle–lower reaches of the Yangtze River with 10–30 main locally planted high-yielding hybrid cultivars used as materials. Compared with rice planted in the middle–lower reaches of the Yangtze River, rice planted in the upper reaches has a longer tillering duration, higher accumulated temperature(≥10℃) during tillering period, but lower accumulated temperature and solar radiation from initial booting to maturity. Yield traits comparison between the upper and the middle–lower reaches of Yangtze River showed that the former had 48.1% more panicles per unit area while the latter had 46.4% more grains per panicle; the rice yield in the former was positively correlated with the seed setting rate and the dry matter accumulation before heading, while the latter was positively correlated with grains per panicle and dry matter accumulation from booting to maturity. Comparison of the same variety Tianyouhuazhan planted in different regions showed there was a significant positive correlation between panicle number and the duration of and accumulated temperature during the tillering period(r=0.982~(**), r=0.993~(**), respectively), and between grains per panicle and accumulated solar radiation during booting period(r=0.952~*). In the upper reaches of the Yangtze River, more than 90% of cultivars with an yield of greater than 11 t ha~(–1) had an effective panicle number of 250–340 m~(–2), and there was a significant negative correlation between seed setting rate and grains per panicle; therefore, the high-yielding rice production in these regions with a long effective tillering period(40 d) should choose varieties with moderate grains per panicle, adopt crop managements such as good fertilizer and water measures during vegetative growth period to ensure a certain number of effective panicles, and to increase the dry matter accumulation before heading. While in regions with a short effective tillering period(20 d) but good sunshine conditions during the reproductive growth period, such as the middle–lower reaches of the Yangtze River, high-yielding rice production should choose cultivars with large panicles, adopt good water and fertilizer managements during the reproductive growth period to ensure the formation of large panicles and the increase of dry matter accumulation after heading.     

Dynamic Development of Aphelenchoides besseyi on Rice Plant by Artificial Inoculation in the Greenhouse

A study was done on the relationship between Aphelenchoides besseyi and the symptoms of small grains and erect panicles. This is an important rice disease in Jiangsu Province, China. A. besseyi was extracted from small grains and erect panicles and cultured artificially, and then inoculated into bud and leaf sheaths of seedlings of two Oryza sativa cultivars, namely Zhendao 2 and Wuyunjing 7 in a greenhouse. The effect on rice growth, in particular the small grains and erect panicles, was revealed by the extent of the disease, seed expansion stages, nematode load, and nematode mortality. In contrast to healthy seedlings, the height, length, and the numbers of spikelets of unhealthy panicles of Zhendao 2 were decreased by 6.7, 16.4, and 13.5%, respectively. Before anthesis, nematodes were attracted to the leaf sheath and apical meristem, nematode load increased by 40%; after anthesis, nematodes occurred in spikelets principally and the number increased by 90.8%. The percentages of infected seeds and nematode load were highest in plump seeds and lowest in empty seeds. Nematode mortality on grain with normal endosperm was lower than seeds with abnormal endosperm. Results indicated that A. besseyi was the pathogen in rice with the symptoms of small grains and erect panicles. Wuyunjing 7 manifests only the small grains and erect panicles symptoms and not the symptoms of leaf white-tip. These symptoms of small grains and erect panicles are new symptom records for the disease caused by A. besseyi on rice.     

不同类型籼稻区对杂交籼稻性状的影响

为明确不同稻作区对杂交籼稻表型的影响, 2014—2015年连续2年对种植于3个不同稻区(双季籼稻区、单季籼稻区和籼粳交错区)的40个籼稻杂交组合的农艺和抗病性状分析。结果表明,双季稻区和交错区对40个籼稻杂交组合农艺性状(生育期、株高、穗长、有效穗、穗总粒数、结实率、千粒重和产量)变化影响很大,而单季稻区的杂交组合性状表现居于双季稻区和交错区之间。双季稻区的穗颈瘟、纹枯病和白叶枯病严重,交错区是穗颈瘟和纹枯病严重。基于农艺性状和发病情况数据,采用特有性简约性分析法分析,40个杂交组合的综合表型在不同稻作区多数呈现连续分布,在交错区87.5%(35/40)的籼稻杂交组合综合表型发生聚集,单季稻区为75.0%(30/40),双季稻区为57.5%(23/40)。在交错区和双季稻区都适宜种植的籼稻杂交组合占比仅为2.5%(1/40),在双季稻和单季稻区都适宜的杂交组合占比为40.0%(16/40)。     

Evaluation of Chinese rice varieties resistant to the root-knot nematode Meloidogyne graminicola

The root-knot nematode Meloidogyne graminicola, which is distributed worldwide, is considered a major constraint on rice production in Asia. The present study used the root gall index and number of nematodes inside the roots to evaluate resistance/susceptibility to M. graminicola in different subpopulations of Oryza sativa(aus, hybrid aus, indica, hybrid indica, temperate japonica, tropical japonica). Nematode development in highly resistant varieties was also evaluated. Analyses of randomly selected 35 varieties showed the number of M. graminicola nematodes inside the roots correlated very strongly(r=0.87, P≤0.05) with the nematode gall index, and the results from pot and field experiments revealed similar rankings of the varieties for resistance/susceptibility. Among the 136 tested varieties, temperate japonica displayed the highest gall index, followed by tropical japonica, indica, hybrid indica, aus, and hybrid aus. Zhonghua 11(aus), Shenliangyou 1(hybrid aus) and Cliangyou 4418(hybrid indica) were highly resistant to M. graminicola under both pot and field conditions. Further examination of nematode development suggested that compared to susceptible rice, M. graminicola penetrated less often into highly resistant varieties and more frequently failed to develop into females. The promising varieties found in the present research might be useful for the breeding of hybrid rice in China and for the further development of practical nematode management measures.     

江苏省水稻"小穗头"发生原因和防治技术研究

近年来,江苏省大面积、多品种水稻普遍发生"小穗头"症状.经室内检测,发现"小穗头"谷粒中含有大量的线虫,而健康稻穗的谷粒中不含线虫.鉴定结果表明水稻"小穗头"中含有的线虫为水稻干尖线虫(Aphelenchoides besseyi),"小穗头"症状是水稻干尖线虫病的一种非典型症状.田间试验表明,应用巴丹、恶线清(16%咪鲜·杀螟)等杀干尖线虫药剂在水稻播种前浸种48～60 h,可有效防治水稻"小穗头"症状发生,其防治效果可达90%以上.     

Dry matter production and panicle characteristics of high yield and good taste indica hybrid rice varieties

Indica hybrid rice (Oryza sativa) production aims to achieve two crucial targets: high yield and good taste. This study selected three types of indica hybrid rice according to grain yield and taste value, including high yield and good taste (HYGT), low yield and good taste (LYGT), and high yield and poor taste (HYPT), to analyze yield components, corresponding growth characteristics, and rice taste quality. When values were averaged across varieties and years, there were almost no differences in taste value between HYGT and LYGT; HYGT showed a significant increase in yield, owing to a higher number of panicles and spikelets per panicle, with a respective increment of 16.2 and 20.6%. The higher grain yield of HYGT compared with LYGT was attributed to three key factors: a higher leaf area index (LAI) during heading, a higher ratio of grain to leaf, and a higher biomass accumulation at maturity. HYGT and HYPT achieved similar high yields; however, HYGT had more panicle numbers and lower grain weight. In addition, HYGT showed a significantly higher taste value than HYPT, attributed to its significantly lower protein and amylose contents, with reductions of 8.8 and 15.7%, respectively. Lower protein and amylose contents might be caused by a proper matter translocation from vegetative organs to panicle. This study suggested that reasonable panicle characteristics and translocation efficiency from vegetative organs to panicle during heading to maturity are the key factors in balancing yield and rice taste quality. These results will provide valuable insights for rice breeders to improve the grain yield and quality of indica hybrid rice.     

超级稻群体籽粒库容特征的初步研究

【目的】探索超级稻群体库容形成及其构成特征。【方法】以具有代表性的5个籼型超级稻为材料,用汕优63为对照,比较研究超级稻群体籽粒库容构成及特征。【结果】 (1)不同试点的超级稻品种均显著或极显著比对照增产,群体颖花量的增加是产量增加的直接原因。培育大穗是超级稻扩大库容量、增加颖花量的主要途径,而增穗并不能扩增群体总颖花量。(2)大穗是通过两种途径协调实现的:一是增加一次枝梗数及其上的平均着粒数,二是增加二次枝梗数但稳定二次枝梗上的平均着粒数; 其中增加二次枝梗数及其总粒数是主要的; 超级稻在一、二次枝梗数增加的同时,通过稳定二次枝梗上的平均着粒数而增加一次枝梗上的平均着粒数,优化颖花分布,提高全穗结实率而增加单穗籽粒重; 超级稻单穗重达4.0 g 以上, 平均比对照增重10.9% 。(3)超级稻产量潜力高,最大库容达870 kg/667m2，显著高于对照,平均增幅近10%；但最高库容有效充实度在品种间、试点间变化较大,并无稳定优势,平均为80.3%，略低于对照，故因种因地栽培是实现超级稻稳定超高产的关键。【结论】超级稻在稳定适宜穗数的基础上通过协调增加一次枝梗数和二次枝梗数及其平均着粒数来增大穗型,通过优化一、二次枝梗上颖花分布来提高结实率从而增加单穗重。     

Combined effect of shading time and nitrogen level on grain filling and grain quality in japonica super rice

There is limited information about the combined effect of shading time and nitrogen(N) on grain filling and quality of rice. Therefore, two japonica super rice cultivars, Nanjing 44 and Ningjing 3, were used to study the effect of shading time and N level on the characteristics of rice panicle and grain filling as well as the corresponding yield and quality. At a low N level(150 kg N ha~(–1), 150 N), grain yield decreased(by 21.07–26.07%) under the treatment of 20 days of shading before heading(BH) compared with the no shading(NS) treatment. These decreases occurred because of shortened panicle length, decreased number of primary and secondary branches, as well as the grain number and weight per panicle. At 150 N, in the treatment of 20 days of shading after heading(AH), grain yield also decreased(by 9.46–10.60%) due to the lower grain weight per panicle. The interaction of shading and N level had a significant effect on the number of primary and secondary branches. A high level of N(300 kg N ha~(–1), 300 N) could offset the negative effect of shading on the number of secondary branches and grain weight per panicle, and consequently increased the grain yield in both shading treatments. In superior grains, compared with 150 N NS, the time to reach 99% of the grain weight(T_(99)) was shortened by 1.6 to 1.7 days, and the grain weight was decreased by 4.18–5.91% in 150 N BH. In 150 N AH, the grain weight was 13.39–13.92% lower than that in 150 N NS due to the slow mean and the maximum grain-filling rate(GR_(mean )and GR_(max)). In inferior grains, grain weight and GR_(mean) had a tendency of 150 N NS150 N BH150 N AH. Under shaded conditions, 300 N decreased the grain weight due to lower GR_(mean) both in superior and inferior grains. Compared with 150 N NS, the milling and appearance qualities as well as eating and cooking quality were all decreased in 150 N BH and 150 N AH. Shading with the high level of 300 N improved the milling quality and decreased the number of chalky rice kernels, but the eating and cooking quality was reduced with increased chalky area and overall chalkiness. Therefore, in the case of short term shading, appropriate N fertilizer could be used to improve the yield and milling quality of rice, but limited application of N fertilizer is recommended to achieve good eating and cooking quality of rice.     

Effects of different mechanical direct seeding methods on grain yield and lodging resistance of early indica rice in South China

Direct seeding of rice has become a main planting method due to the low labor input and high economic benefit in South China. Dry direct seeding(DDS) has been widely used for single-season rice planting establishment. However, few studies have examined the performance of early-season indica rice under mechanical dry direct seeding. A two-year field experiment was conducted with two indica rice cultivars(i.e., Zhongjiazao 17 and Zhuliangyou 819) to study lodging characteristics and grain yield formation under DDS, flooded direct seeding(FDS) and wet direct seeding(WDS) patterns. The results showed that the annual grain yield in DDS was higher by 14.42–26.34% for cultivar ZLY819 and 6.64–24.58% for cultivar ZJZ17 than in WDS and FDS, respectively, and these increases were mainly attributed to the improvement of the panicles. The DDS pattern significantly increased the seedling emergence rate of early indica rice cultivars, and increased total dry weight and crop growth rate. Meanwhile, shorter basal internodes, better stem diameter and stem wall thickness and lower lodging index were found in DDS in contrast to FDS and WDS. In particular, DDS improved the stem lodging resistance. Our results suggested that the appropriate direct seeding method was beneficial for improving the grain yield and lodging resistance of early indica rice.     

盐胁迫下OsDSR2RNAi转基因水稻的主要农艺性状分析

为探究盐胁迫下 OsDSR2 抑制表达后对水稻主要农艺性状和产量的影响,进一步阐明 OsDSR2 参与调控水稻耐盐机制,以野生型植株中花11(ZH11)和 OsDSR2 RNAi转基因水稻不同株系DR14和DR20为试验材料,植株幼穗分化期进行0.15mol/L盐胁迫处理,待植株完熟后测定穗长、每穗总粒数、每穗实粒数、结实率、单株穗数、单株粒质量、千粒质量等主要农艺性状,并进行相关性和主成分分析。结果表明,盐胁迫后 OsDSR2 RNAi转基因水稻的单株穗数、结实率均显著高于野生型ZH11,正常条件下, OsDSR2 RNAi转基因水稻单株粒质量均显著低于野生型ZH11,盐胁迫后二者均降低但无显著性差异。与正常条件下相比,盐胁迫处理后 OsDSR2 RNAi转基因植株的千粒质量与每穗实粒数呈显著负相关性,单株粒质量与穗长、结实率、千粒质量呈负相关性,单株穗数与穗长、结实率呈负相关性,单株粒质量与每穗总粒数呈正相关性;结实率与穗长、每穗总粒数呈负相关性。盐胁迫处理后 OsDSR2 RNAi转基因水稻第一、二主成分中,分别是单株粒质量和结实率特征向量最大。综上,盐胁迫下 OsDSR2 的抑制表达主要通过抑制水稻植株的单株穗数、结实率和单株粒质量的降低,协调单株粒质量与单株穗数、结实率、千粒质量的关系以及结实率与千粒质量、单株穗数的关系,从而调控盐胁迫下水稻的产量。     

Effects of seedling age on the growth stage and yield formation of hydroponically grown long-mat rice seedlings

Understanding the characteristics of rice productivity is of great importance for achieving high yield formation. However, such traits have not yet been studied for different ages of hydroponically grown long-mat rice seedlings(HLMS), which constitutes a new method of seedling cultivation. Field experiments were conducted to evaluate the effects of seedling age on the growth stage, photosynthesis characteristics, dry matter production, and yield of HLMS. A conventional japonica rice cultivar(Wuyunjing 24) and an indica hybrid rice cultivar(6 Liangyou 9368) were used as test materials. The results showed that the whole phase was shortened by 13–15 days for young seedlings(13-day-old) compared with old seedlings(27-day-old), which occurred because the growth process accelerated with the transplantation of young seedlings. As seedling age increased, the dry matter weight of stems of individual plants and of the population increased at the transplanting stage but decreased at the maturity stage(MS). Compared with that of 27-day-old seedlings, the average ratio of panicle weight to total plant dry weight of 13-day-old seedlings during a 2-year period increased by 3.71% for Wuyunjing 24 and by 3.78% for 6 Liangyou 9368 at the MS. Moreover, as seedling age increased, the leaf area index and photosynthetic potential decreased for both cultivars, and the photosynthetic rate markedly decreased at the heading stage(HS). With the exception of that of Wuyunjing 24 from the jointing stage to the HS in 2014, the crop growth rate was higher for young seedlings than for old seedlings. Grain yield significantly decreased with seedling age, but no significant difference was detected between the 13-and 20-day-old seedlings for either cultivar. Therefore, equilibrious and high biological yield formation, vigorous growth in the late stages, and high photosynthetic production capacity are important characteristics and causes of the efficient and sustainable output of photosynthetic systems and for achieving high yield formation in young transplanted seedlings(13–20-day-old).