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10 November 2008, Volume 22 Issue 6 Previous Issue    Next Issue
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研究报告
综述与专论
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Analysis on Expression Patterns of the Family Members of Rice Bacterial Blight Resistance Gene Xa3/Xa26 XU Lei,LI Xianghua,WANG Shi ping* 2008, 22(6): 559-559～563 .  Abstract ( )   PDF (1262KB) ( )   The bacterial blight resistance gene Xa3/Xa26 belongs to a multigene family. To predict whether this multigene family contains other resistance gene(s) and the putative function sites of these genes, the expression patterns of the family members were analyzed. The promoters of 13 Xa3/Xa26 family members, MRKa, Xa3/Xa26, MRKc, TRKa, TRKb, TRKc, 9RKa, 9RKb, 9RKe, NRKa2, NRKe, NRKf1, and NRKf3 isolated from indica rice varieties Minghui 63, Teqing and 9311 and japonica rice variety Nipponbare, with the reporter gene encoding green fluorescent protein (GFP) were connected and these constructs were separately transferred into rice by Agrobacteriummediated transformation. Examination of GFP expression in transgenic plants showed that the Xa3/Xa26 family members had similar expression pattern. These members mainly expressed in the cells of vascular systems and cells around vascular systems in different tissues of rice. The expressional characteristic of Xa3/Xa26 family members fits the function for the genes conferring resistance to Xanthomonas oryzae pv. oryzae, the vascular pathogen. The expressional characteristic also provided basis for continued generation of new disease resistance genes from this family during evolution.

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Development of Molecular Markers for Sbe Gene in Association with Starch Characteristic in Rice LI Gang,#,DENG Qiming,#,WAN Yingxiu,LI Shuang cheng,XIAO Yong,ZHOU Peng,WANG Shiquan,LI Ping 2008, 22(6): 564-564～570 .  Abstract ( )   PDF (1965KB) ( )   Based upon the genomic sequence difference between the indica rice variety 9311 and the japonica rice variety Nipponbare, a total of nine molecular markers for starch branching enzyme gene(Sbe) were successfully developed. All the markers were utilized for genotypic screening and further analysis of the correlation between genetic polymorphisms of Sbe1 and Sbe3 genes and the rice starch characteristics. The genetic polymorphism of the markers had no influence on starch physiochemical traits, that is these allelomorphism variation sites of Sbe gene had no influence on the starch traits of nonglutinous rice. There were six markers which could be used to accurately identify indica rice varieties with a reliability over 80%. Meaning of marker development and molecular marker assisted selection were also discussed.

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Co-segregation Analysis Between TDNA Tag and Character of Small Grain Dwarf Mutant in Rice MA Yuyin,ZHANG Yafang,PAN Cunhong,LI Aihong,WU Xujiang,ZUO Shimin,CHEN Zongxiang,WU Changyin,PAN Xuebiao 2008, 22(6): 571-571～577 .  Abstract ( )   PDF (1649KB) ( )   A small grain dwarf (sgd) mutant was identified in the segregated population from a TDNAtag rice line. Genetic analysis of this mutant was conducted for cloning and functional research of the gene. Multiple TDNA insertion copies in this line were confirmed, and one of them had been homozygous in T3 segregation population. As a result, it was impossible to detect cosegregation between the tag and sgd merely depended on the specific PCR primer from TDNA in T3 and successively generations. However, a flanking sequence from one of TDNA insertion sites was obtained by TAILPCR, and was confirmed to be cosegregated with sgd in consecutively segregated generations.

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Genetic Analysis and Molecular Mapping of LightSensitive RedRoot Mutant in Rice (Oryza sativa) ZHANG Junzhi,LIU Xiao,LI Chao,XIAO Ke,DONG Yanjun* 2008, 22(6): 578-578～582 .  Abstract ( )   PDF (1213KB) ( )   The lightsensitive redroot mutant, designated as HG1, was newly observed in an indica rice variety, Nankinkodo, when the roots were exposed to natural light under hydroculture conditions. The root color of the mutant began to turn slightred when the roots were exposed to the light at the intensity of 29 μmol/（m2·s）, and turned darkred at 180 μmol/（m2· s）, which suggested that the root color of the mutant was very sensitive to light. Furthermore, genetic analyses showed that the character of lightsensitive redroot in the HG1 mutant was controlled by a single dominant gene, tentatively designated as Lsr. With the SSR markers, Lsr gene was mapped between RM252 and RM303 on chromosome 4 with the genetic distances of 9.8 cM and 6.4 cM, respectively. The results obtained from the study could be useful for fine mapping and cloning of Lsr gene in rice.

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Correlation Between Parents and F1 and Combining Ability of Parents in Seed Dormancy for indica Hybrid Rice XU Baoqin,LU Zuomei 2008, 22(6): 583-583～589 .  Abstract ( )   PDF (49KB) ( )   Dormancy indexes of hulled and dehulled seeds were investigated by using 109 F1 hybrids and their 19 cytoplasmic male sterile(CMS) lines and 9 restorer lines in indica hybrid rice. The seeds of each F1 and the parents were harvested at 35 days after flowering. Meanwhile, combining ability was analyzed in 25 combinations made by 5 CMS lines and 5 restorer lines (NCⅡ genetic design). The results showed that the seed dormancy index of F1 was positively and highly significantly correlated with those of their parents and midparent value. Out of the 109 combinations, 82 showed midparent heterosis, and 43 heterobeltiosis. Seed dormancy index of F1 and their parents declined dramatically in dehulled seeds compared with hulled seeds, indicating that the hull played an important role in seed dormancy. However, the trend was similar in hulled and dehulled seeds in terms of relationship between F1 and their parents in seed dormancy. The influence of hull on seed dormancy depended mainly on F1 genotype, not on hull itself of maternal parent. The variance of general combining ability(GCA) in female and male parents occupied 592% and 31.1% of total variance, respectively. The variance of specific combining ability(SCA) in combinations occupied 97% of total variance, indicating that gene additive effects were principal. Among the 5 CMS lines, Ⅱ112A had the highest GCA effect for seed dormancy, followed by D62A. Among the 5 restorer lines, IR112 had the highest GCA effect for seed dormancy followed by 2786. They were excellent materials as parents for breeding F1 hybrid rice with stronger seed dormancy.

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Breeding of Rice Restorer Lines Carrying Blast Resistance Gene Pi25 by MarkerAssisted Selection ZHOU Haipeng,#,ZHAN Xiaodeng,#,CAI Rongyao,CHENG Shihua,CAO Liyong 2008, 22(6): 590-590～596 .  Abstract ( )   PDF (848KB) ( )   Three recombinant inbred lines (RILs) carrying rice blast resistance gene Pi25 from the combination Zhong 156/Gumei 2 were crossed with highyielding restorer lines, 9308 and 311. The seeds were collected and advanced by single seed descent, and six RIL populations at the F6 generation were obtained and used for the study. Based on the previously reported genetic map, four additional SSR markers RM3330, RM564, RM3628 and RM6298 were added to the interval harboring Pi25 on rice chromosome 6. Relied on the marker genotyping of RM3330 and A7, 109 Pi25 homozygous lines were selected from the six RIL populations. Markerassisted selection analysis was carried out on the acquired 109 Pi25 homozygous lines using existing markers linked to fertility restoring genes. As a result, twenty restorer lines resistant to blast were obtained. Studies on fertility restoring ability of the 20 restorer lines concluded that the seedsetting rate of crosses between these restorer lines and cytoplasmic male sterility lines (Zhong 9A and Ⅱ32A) reached a normal level. In addition, three populations were selected to be artificially inoculated with a regionally prevalent isolate 05201 of Magnaporthe grisea to evaluate the accuracy of markerassisted selection. The result manifested that simultaneous selection of the markers flanking the gene on both sides could increase the selection accuracy significantly.

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Reducing Amylose Content of Hybrid Rice Xieyou 57 by Molecular MarkerAssisted Selection CHEN Sheng ,NI Dahu,LU Xuzhong,SONG Fengshun,ZHANG Shilu,WANG Zongyang,CAI Xiuling,LI Zefu,WANG Xiufeng,LI Li,YANG Jianbo 2008, 22(6): 597-597～602 .  Abstract ( )   PDF (1073KB) ( )   To lower the high amylose content of hybrid rice Xieyou 57 (Xieqingzao A/057), Xieqingzao B (the maintainer line of Xieqingzao A) was used as recurrent parent and crossed with a donor parent with low amylose content. PCRAcc Ⅰ molecular marker was applied during backcross to identify three Wx genotypes, i.e. GG, GT and TT. Then the genotypes, the amylose contents and agronomic traits of the four combinations, Xieqingzao B(GG)/057(GG), Xieqingzao B(GG)/057(TT), Xieqingzao B(TT)/057(GG), Xieqingzao B(TT)/057(TT) were detected, respectively. The amylose contents of the hybrids with heterozygous GTWx, i.e. Xieqingzao B(GG)/057(TT) and Xieqingzao B(TT)/057(GG) is 19.3% and 19.2% respectively, lower than that of Xieqingzao B(GG)/057(GG)(26.1%). The amylose contents of different seeds in the two hybrids with heterozygous GTWx differed greatly.The combination of Xieqingzao B(TT)/057(TT) with homozygous TTWx not only showed a decreased amylose content(12.5%) accompanied by increased gel consistency, but also had an improved uniformity in amylose contents among different seeds.

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Growth Characteristics of Rice under Simplified Cultivation with Wheat Residue Return ZHANG Hongxi,ZHAO Buhong ,DU Yonglin ,TAN Changle,DAI Zhengyuan,JI Hongjuan,WANG Baohe,ZHOU Changhai 2008, 22(6): 603-603～609 .  Abstract ( )   PDF (3345KB) ( )   With japonica rice Yangfujing 8 as material, dry matter production, yield formation and the related physiological traits of rice under simplified cultivations (direct seeding, mechanical transplanting and parachute transplanting) with wheat residue return and wheat residue removal were investigated. Compared with the rice plants under wheat residue removal, the panicle number of rice plants under wheat residue return was decreased slightly, whereas the number of grains per panicle, seedsetting rate and 1000grain weight were all increased, leading to a significant increase in grain yield. Under wheat residue return, number of stems and tillers of rice was much lower at all the growth stages, and the photosynthetic potential, leaf area index and dry matter accumulation were lower before the heading stage but higher after heading stage than those under wheat residue removal. For rice plants under wheat residue return, the rootshoot ratio was higher at all the growth stages, and the high efficient leaf area and its ratio to total leaf area at the heading stage, the grainleaf ratio, the exportation and transportation rates of carbohydrates stored in stems and sheaths and the harvest index were all higher than those for rice plants under wheat residue removal. Moreover, the root activity, root bleeding, photosynthetic rate and ATPase activity in grains of rice plants under wheat residue return were also higher than those of rice plants under wheat residue removal during grain filling stage. The physiological causes of highyielding rice under wheat residue return were discussed, and the key regulatory approaches under wheat residue return in rice were put forward.

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Effects of Nitrogen Level and Seeding Density on Seeding Quality of indicaType SuperHigh Yielding Hybrid Rice LI Ganghua ,LI Dean,NING Jiachao ,HUANG Qingyu ,GU Wei ,YANG Congdang ,WANG Shaohua ,LING Qihong ,DING Yanfeng 2008, 22(6): 610-610～616 .  Abstract ( )   PDF (6228KB) ( )   In order to investigate the effect of nitrogen level, seeding density and seedling age on seedling quality of rice, a twofactor experiment including four N levels (10.3，20.7，31.0 and 41.4 g/m2) and four seeding densities (353， 706， 1059 and 1412 plants/m2) was conducted at Taoyuan town, Yongsheng county, Yunnan Province. Dynamic of leaf age, tiller number, dry weight, leaf SPAD value of seeding and leaf area index (LAI) in seedling nursery were investigated using an indica hybrid rice, Xieyou 107 as material. The low seeding densities or high N levels decreased the effective accumulated temperature for leaf emergence on stem and accelerate the leaf emergence, especially for seeding densities; Tiller number per seedling decreased with the development of seedling under high seeding density or low N level, whereas increased till 27 days after sowing then decreased under low seeding densities or high N levels; Nitrogen application promoted the emergence of new tillers, the maintenance of tiller with more than three leaves and the increase of LAI in seedling nursery, dry weight and N content of plant; The increased seeding density had negative effects on seedling quality indices, including the emergence of new tillers, the maintenance of tillers with more than three leaves, dry weight and N content of plants whereas showed positive effects on the LAI of seedling nursery, and the effects were more obvious than nitrogen treatments.

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Simulation on Photosynthetically Active Radiation Distributing in Rice Canopy With Rolled Leaves and Its Optimum Leaf Rolling Index HU Ning,LU Chuangen ,YAO Kemin ,ZOU Jiangshi 2008, 22(6): 617-617～624 .  Abstract ( )   PDF (3783KB) ( )   By replacing leaf area index (LAI) with effective leaf area index (ELAI) through introduction of leaf rolling index (LRI), the distribution of photosynthetically active radiation (PAR) in the canopy of three hybrid rice combinations, Liangyou E32 with high leaf rolling index, Liangyoupeijiu with medium leaf rolling index and Shanyou 63 with nonrolled(normal) leaves, was simulated. The results showed that the model based on ELAI could predict more accurately than that based on LAI. PAR interception, conversion and utilization efficiency of the three combinations were studied and their each optimal LRI and LAI were evaluated. The PAR utilization efficiency of Liangyou E32 was lower due to excessive rolled leaves and less ELAI, and that of Shanyou 63 was also lower because of the faulty PAR interception and lower photosynthetic rate and saturation point at lower layer in the canopy. Compared with the other two combinations, Liangyoupeijiu showed more appropriate distribution of PAR interception conversion efficiency in canopy with higher PAR utilization efficiency. The optimal LRI and LAI for Liangyoupeijiu were 0.11 and 7.6, respectively, which were close to the observed values, 0.11 and 7.9, respectively. However, the optimum LAI of 9.8 for Liangyou E32 and 6.2 for Shanyou 63 were larger or smaller than those under the current plant density, which led to lower PAR utilization efficiency. The optimum LRI of the three hybrids was concluded as 008-012, close to the actual LRI of Liangyoupeijiu.

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A Simulation Study on Leaf Age and Leaf Area Index in Rice YE Hongbao,MENG Yali,TANG Liang,ZHU Yan,CAO Weixing* 2008, 22(6): 625-625～630 .  Abstract ( )   PDF (2208KB) ( )   Based on the field experiments using different type rice varieties under different sowing dates and nitrogen application levels, the leaf age and leaf area index (LAI) simulation models were established. A power function was used to describe the nonlinear relationship between leaf appearance and accumulated thermal time after sowing (TTS). The LAI model contained two consecutive phases: at exponential expansion phase (LAI<1.6), LAI increased exponentially with the accumulated growing degree days after sowing (GDD) and was regulated by the nitrogen level; when LAI≥1.6, leaf area expansion was quantified on the bases of specific leaf area (SLA) and green leaf dry weight. SLA was mainly determined by GDD and nitrogen nutrition index, and green leaf dry weight was calculated as the product of its partitioning index and shoot dry weight. Validation of the models using the experiment data with a wide range of ecological and cultivated conditions showed that the two models could accurately simulate the leaf appearance and LAI dynamic under different environments. Thus, the models might be widely adaptable and applicable, which needs only a few and simple parameters.

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Laboratory Screening of Alternatives to Highly Toxic Insecticides Against the Rice Leafroller, Cnaphalocrocis medinalis AO Zhongwen ，#,TAO Lingmei，#,SU Jianya,GAO Congfen,CHANG Hong,ZHOU Libang,SHEN Jinliang ,LIU Xue,YANG Jun 2008, 22(6): 631-631～636 .  Abstract ( )   PDF (42KB) ( )   To screen alternative insecticides for controlling the rice leafroller, Cnaphalocrocis medinalis(Guenée), the toxicities of 29 insecticides belonging to 8 classes against the thirdinstar larvae of the rice leafroller collected from Nanning City, Guangxi Zhuang Autonomous Region and Nanjing City, Jiangsu Province, China were measured by the Potterspraying method. The toxicity levels of the eight classes insecticides were as follows: antibiotic insecticides≥phenyl pyrazole derivative insecticides≥oxadiazine insecticides≥ insect growth regulator insecticides≥organophosphorus insecticides, pyrethroids insecticides≥organochlorine insecticides≥nereistoxin insecticides. Emamectinbenzoate had the highest toxicity against the thirdinstar larvae of the rice leafroller, with LC50 ranging from 0.2 to 0.8 mg/L; while the LC50 of fipronil, indoxacarb, JS118, butylenefipronil, tebufenozide, chlorfluazuron and hexaflumuron were from 1.8 to 53 mg/L. Ten novel insecticides (i.e. emamectinbenzoate, ivermectin, abamectin, fipronil, indoxacarb, JS118, butylenefipronil, tebufenozide, chlorfluazuron, hexaflumuron) and a few organophosphates (i.e. quinalphos, phoxim, profenofos, chlorpyrifos, pyridaphenthion) were recommended to further field trials. Furthermore, the management strategies of the rice leafroller were discussed.

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Impacts of Ten Herbicides on Growth and ShrunkGrain Panicle Formation of Rice Wuyujing 3 YUAN Shuzhong,LU Zhenlong,ZHU Qingsen,YANG Jianchang 2008, 22(6): 637-637～642 .  Abstract ( )   PDF (40KB) ( )   The impacts of ten herbicides on the plant height, tiller number and shrunkgrain panicle formation of a japonica rice variety Wuyujing 3 were studied in a pot experiment. In the soil treatment experiment, the plant height of rice was remarkably inhibited, but the tiller number of rice was not significantly influenced by acetochlor at the doses of 225 and 337.5 g/hm2 or by acetochlor (225 g/hm2) + bensulfuronmethyl (22.5 g/hm2) at 10 and 20 days after treatment. There were no significant differences in plant height and tiller number of rice between herbicide for soil treatment and the water control at 40 days after treatment. The plant height of rice was significantly inhibited at 10 and 20 days after treatment with chlorsulfuron (0.375, 0.75 and 1.5 g/hm2) and at 40 days after treatment with metsulfuronmethyl (0.75 and 1.5 g/hm2). The tiller number was not significantly influenced by chlorsulfuron or metsulfuronmethyl at 40 days after treatment. Foliar treatment of herbicides had no significant influence on the plant height and tiller number of rice. Additionally, the shrunkgrain panicle with typical symptom was not observed. Consequently, it was suggested that the herbicide was not a direct factor causing shrunkgrain panicle in Wuyujing 3.

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Effects of Triazophos on Volatiles from Rice Plants Infested by Cnaphalocrocis medinalis LU Haiyan,LIU Fang*,BAO Shanwei,SONG Ying,SHI Ximin,ZHU Shude,ZHANG Qing 2008, 22(6): 643-643～649 .  Abstract ( )   PDF (47KB) ( )   The volatiles from rice plants infested by Cnaphalocrocis medinalis were studied under triazophos application. Thirtysix components were collected from headspace of rice plants by solid phase microextraction, 14 of which were identified by gas chromatography coupled with mass spectrometry, and the major components are terpenes and their oxides (11 kinds). Four of the identified components including isoledene, (-)αcedrene, (+)βcedrene and cedrol have not been reported in rice plants. Different triazophos treatments did not result in the emission of new compounds, but the relative proportions (percent of total peak area) among the compounds in the blend were altered. The proportions of 5 components (13.9%) had significant differences under triazophos treatment at three levels. The proportions of 27 components (75.0%) changed at different days after triazophos treatment. Furthermore, the proportions of 32 components (88.9%) were significantly changed due to the interactions between triazophos and rice varieties, densities of C. medinalis.

综述与专论

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Progress and Prospects of Breeding by Gene Design in Rice GUO Longbiao,CHENG Shihua*,QIAN Qian* 2008, 22(6): 650-650～657 .  Abstract ( )   PDF (1399KB) ( )   : Progress in molecular markers, gene engineering and genomics are beneficial to direct selection and crop breeding by design. Breeding by design is a concept that aims to control all allelic variation for all genes of agronomic importance. This concept can be achieved through a combination of precise genetic mapping, highresolution chromosome haplotyping and extensive phenotyping. Thanks to marker technology and software tools available today, and the finemapped/cloned genes in rice and their related GP data bank, this goal can now be achieved. Some related techniques concerning molecular breeding and breeding by genedesign, a highlight of breeding by genedesign and progress in functional research for key genes and their molecular utilization in rice breeding are presented in the paper. In addition, the prospects of rice genedesign breeding are discussed.

研究简报

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Genetic Analysis and Gene Mapping of a Twisted Hull Mutant in Rice LI Jinbo ,XIA Mingyuan ,WAN Bingliang ,DU Xueshu ,ZHA Zhongping ,YU Dazhao ,QI Huaxiong 2008, 22(6): 658-658～660 .  Abstract ( )   PDF (738KB) ( )   A twisted hull rice mutant was found in the progeny of a breeding population. Genetic analysis indicated that the mutant phenotype was controlled by a single recessive gene (temporarily designated as Osth). To map OsTH(t) gene, an F2 population was established by crossing the Osth mutant with R725, an indica rice variety with normal hulls. Finally, OsTH(t) was located between the SSR markers RM14128 and RM208 on the long arm of chromosome 2 at the genetic distances of 1.4 cM and 2.7 cM, respectively. These results provides the foundation for further fine mapping, cloning and functional analysis of OsTH(t) gene.

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Response of Malondialdehyde Content in Leaves and Yield Traits of Super Hybrid Rice to Water Deficit ZHANG Weixing ,ZHU Defeng ,ZHAO Zhi ,LIN Xianqing ,ZHANG Yuping,CHEN Huizhe 2008, 22(6): 661-661～664 .  Abstract ( )   PDF (548KB) ( )   With three super hybrid rice combinations (Liangyoupeijiu, Guodao 6 and Ⅱ you 602) and a conventional hybrid rice combination Shanyou 63 as materials, response of the malondialdehyde (MDA) content in leaves and yield traits for these rice materials to water deficit from panicle initiation to 30 days after flowering(DAF) was studied in a pot experiment. Water deficit accelerated membrane lipid peroxidation, thus led to an increase in MDA content in rice leaves. Moreover, the MDA content rose with the leaf position down. The MDA contents in the 3rd leaf from top was the highest, followed by the 2nd leaf from top and the flag leaf. The MDA content in rice leaves was enhanced under water deficit, especially in the lower position leaves, which caused damage to enzyme and cell membrane, ultimately affected cell normal physiological metabolism. Water deficit had various influence on yield and its components. The yield reduction due to water deficit during 0-15 DAF and 15-30 days after panicle initiation(DAPI) amounted to 27.5% and 26.9%, respectively, followed by 15-30 DAF(24.2%). Compared with normal water supply, the yield of rice under water deficit declined significantly, which was mainly caused by obvious reduction of seed setting rate and 1000grain weight. The changes in the MDA content responded to water deficit correlated with plant growth and development, final output of rice grains at a certain extent. Water deficit exerted less influence on MDA content in rice leaves and yield traits of super hybrid rice combinations than that of conventional hybrid rice combination. Based on the relationship between stress degree and effect, stress lasting time and effect, the opinion on the relationship between growing course and effect was put forward and discussed.

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Effects of Nitrogen Forms on Root Morphology and Phosphate Uptake in Rice LI Baozhen ,WANG Songwei ,FENG Huimin ,XU Guohua 2008, 22(6): 665-665～668 .  Abstract ( )   PDF (3296KB) ( )   A hydroponic experiment was conducted to study the effect of N forms (NH4+,NO3- and NH4NO3) on root morphology and P uptake in rice. The results indicated that the root morphology of low P starved rice was affected very significantly by N forms. In comparison with ammonium as sole N source, the ammonium nitrate nutrition increased root length, root surface area, root density, and total P uptake. In comparison to either ammonium or nitrate alone, mixture supply of the two forms of N increased transport of P from roots to the aboveground parts. It was suggested that the improved P uptake by mixture supply of both ammonium and nitrate were partially due to the stimulation of root growth.

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Inhibitory Effect of Different Rice Varieties on Weeds in Paddy Field LI Gui,WU Jinglun*,WANG Yizhuan,LIU Liping 2008, 22(6): 669-669～672 .  Abstract ( )   PDF (31KB) ( )   Field experiments were conducted to study the competition between rice and weed, and the differences in inhibitory effects of rice on barnyardgrass \[Echinochloa crusgalli(L.) Beauv.\], sedge weeds and broadleaf weeds by using 7 rice varieties. The inhibitory effects of Yangdao 6 and PI312777 were 79.74% and 70.26% on weed germination, and 91.84% and 8294% on weed dry weight, respectively. Xudao 4 could also significantly inhibit weed germination and growth, which led to reduced biomass accumulation of weeds. At the same time, the results showed that the inhibitory effects of the tested rice varieties on the barnyardgrass roots were significantly higher than that on the shoots. The same tendency was found in the inhibitory effect on both total dry weight and shoot dry weight of barnyardgrass .