Inheritance and genetic linkage analysis of a firm-ripening tomato mutant

The tomato cv. ‘Santa Clara’ is widely cultivated among tomato producers in most of the South‐east of Brazil. Recently, some plants of this cultivar were identified with morphological alterations in both vegetative and reproductive organs. These plants showed firm (firme) ripe fruits, slow and delayed ripening. They also had yellow leaves associated with precocious senescence and flowers with pale stigmas. The objective of this work was to determine the genetic model of inheritance for this mutation and to evaluate its effects on shelf life and loss of firmness in mature fruits, as well as analyse the occurrence of genetic relationships between this putative mutant and other pleiotropic mutants. Mutated plants were crossed with the non‐mutant cv. ‘Santa Clara’ and some previously described pleiotropic mutants. Seeds of F₁ and F₂ generations and backcrosses were obtained for the segregation analysis. Morphological characteristics modified by this mutation are governed by a recessive gene with pleiotropic effects. In addition, the test of allelism showed a lack of genetic complementation between the ‘firme’ mutant and lutescent‐2 mapped on chromosome 10. Fruits of the ‘firme’ mutant had a slower rate of softening compared with the cv. ‘Santa Clara’ and its hybrids. The fruit shelf life of the mutant ‘firme’ was significantly superior to the other genotypes. No maternal effect was detected in either qualitative or quantitative characteristics. Based on the data, the mutation ‘firme’ in the cv. ‘Santa Clara’ is located in the region containing the l‐2 locus, which promoted alterations in ripening and post‐harvest physiology of fruits. The mutation ‘firme’ may represent a new allele of the gene lutescent‐2 or a gene linked to physiological events of fruit ripening.     

General combining ability and heterosis regarding the phytochemical properties in strawberry (Fragaria × ananassa) hybrids

Strawberries are a common and important fruit in human diet because of their high content of essential nutrients and beneficial phytochemicals, which have relevant biological activity in human health. In this study, six cultivars and 15 selected F₁ hybrids between S₄ inbred lines and tester (cv. ‘Dukat’) were evaluated in a field trial over a period of two consecutive years. The amounts of total anthocyanin, phenolics and vitamin C in fruits and antiradical activity were analysed. General combining ability (GCA) and mid‐parent heterosis were also determined for those characteristics. Among all the genotypes tested, the inbred lines of ‘Senga Sengana’ 17 showed the highest breeding value based on GCA for all studied traits. Estimated heterosis varied among genotypes tested. The highest heterosis in terms of vitamin C occurred in the offspring of clone 1387 18‐15 × ‘Dukat’, but with regard to phenols and antiradical activity in hybrid ‘Teresa’ 18‐15 with cv. ‘Dukat’. This study revealed that the differentiation in chemical composition of strawberry fruits between genotypes is clearly dependent on individual genotype combinations and demonstrated the presence of heterosis in phytochemical contents in some specific genotypic combinations.     

Oxidative stress indicators as selection tools for salt tolerance

Oxidative stress indicators, malondialdehyde (MDA) accumulation and chlorophyll retention, were tested as tools for salt‐tolerance screening in Chloris gayana (Kunth), a forage grass exhibiting inter‐ and intra‐cultivar variability in the response to salt stress. Three types of experimental system were compared, salt shock, gradual salt treatment and leaf segments floated on control and saline solutions. Results followed the same trend in the three systems, but leaf segments or gradually salinized plants are the most convenient. Lower mean MDA and higher mean chlorophyll content were found under salinity in cv. ‘Katambora’, which is considered, from previous field trials, to be more salt tolerant than cv. ‘Boma’. Nevertheless, chlorophyll content did not give consistent results in other tests and it is not recommended for selection purposes. Within cv. ‘Boma’, clones rating higher in a salt tolerance evaluation under greenhouse conditions had lower MDA content under salinity and lower mean MDA ratios between salt‐treated and control samples. The survival of 80‘Boma’ plants under increasing NaCl concentration was assessed and MDA was measured in the leaves of very plant before the final NaCl level was reached, to assess whether it was predictive of survival capability. MDA values were significantly lower in the group surviving longer, thus, a selection based on low MDA values would have enriched the original population with more tolerant individuals.     

Differential Physio‐Biochemical Responses to Cold Stress of Cold‐Tolerant and Non‐Tolerant Grapes (Vitis L.) from China

There are many grape species exhibiting differences in cold tolerance in China. ‘Zuoshan1’ (Vitis amurensis Rupr. cv. Zuoshan1), one kind of the most cold tolerant grapes, can endure ?40 to ?50 °C, whereas, ‘Maoputao’ (Vitis quinqanguoari Rehd. cv. Maoputao) is sensitive to the cold stress. To understand the physiological mechanism, we investigated responses of both species to a range of decreasing temperatures under the controlled condition. The cold‐tolerant ‘Zuoshan1’ showed higher accumulation of abscisic acid than non‐tolerant ‘Maoputao’, which was correlated with a more dramatic increase in solutes including sugars, proteins at early stage of our detection. At latter stages, these solutes showed more decline in ‘Zuoshan1’. Meanwhile, earlier leaf yellowing and necrosis of ‘Zuoshan1’ were detected with concomitant decrease in the chlorophyll (Chl) content along with remarkable increase in electrolyte leakage and malondialdehyde, which indicated that the earlier leaf senescence occurred to ‘Zuoshan1’. Based on the leaf morphology and parameter investigation, it was concluded that cold‐tolerant grape ‘Zuoshan1’ made quicker responses to the low temperature (LT), indicating it sensed the cold‐signal more strongly than the non‐tolerant grape ‘Maoputao’. Therefore the ability to take more active response to cold stress contributes to the higher tolerance in ‘Zuoshan1’.     

Introduction of aromatic fragrance into cultivated tomato from the peruvianum complex'

This study was performed to introduce the distinct aromatic fragrance of Lycopersicon peruvianum LA 1554 into the cultivated tomato, Lycopersicon esculentum. The strong breeding barriers existing between these two distantly related species were circumvented by the ovule selection and culture method. A large BC₁F₁ population was developed and among 127 plants, 36 were self‐compatible and yielded fruits. Fruits of some of these selected plants were found to be enriched with a sweet aromatic flavour. Sensory evaluation of the fruit aroma of these selected plants was performed by a panel of 12 members against one of the best consumer‐rated Japanese commercial tomato cultivars, ‘Momotaro’. Although extensive variation was observed in fruit‐aroma in the BC₁F₁ population, panel opinion on ‘flavour‐desirability’ significantly favoured the BC₁F₁ fruits of some selected plants over the cv. ‘Momotaro’. Therefore, it can be concluded that the aromatic fragrance of a ‘L. peruvianum’ accession has successfully been introduced into the cultivated tomato gene pool.     

Physiological Response to Heat Stress During Seedling and Anthesis Stage in Tomato Genotypes Differing in Heat Tolerance

Tomato cultivars differ in their sensitivity to heat stress, and the sensitivity depends on the developmental stage of the plants. It is less known how heat stress affects tomato at the anthesis stage in terms of leaf physiology and fruit set and whether the ability of tomato to tolerate heat at different developmental stages is linked. To investigate photosynthetic gas exchange characteristics, carbohydrate content and fruit set during heat stress, a thermo‐tolerant cultivar (‘LA1994’) and a thermo‐sensitive cultivar (‘Aromata’) were studied at the seedling and anthesis stage. The photosynthetic parameters, maximum quantum efficiency of photosystem II (F_v/F_m), chlorophyll content, carbohydrate content and fruit set were determined in plants grown at 26/18 °C (control) and 36/28 °C (heat stress). The physiological responses including net photosynthetic rate (P_N), chlorophyll content and F_v/F_m decreased in ‘Aromata’ at both developmental stages during heat stress, whereas they were unaltered in ‘LA1994’ during heat stress as compared to the respective control. This was accompanied by lower contents of glucose and fructose in mature leaves of ‘Aromata’ at the seedling stage under heat stress. In contrast, the glucose content increased while the fructose content was unaltered in mature leaves of ‘LA1994’ at the seedling stage under heat stress. High temperature induced a similar change in carbohydrate content in the young leaves of both cultivars at anthesis. The fructose and sucrose content were unaffected in the mature leaves of ‘Aromata’ but significantly increased in ‘LA1994’ under heat stress at anthesis. The heat stress treatment decreased pollen viability and inhibited fruit set due to flower wilting and abnormal abscission in ‘Aromata’, whereas fruit set was not inhibited in ‘LA1994’. A decrease in chlorophyll content, photosynthesis and carbohydrate content in the mature leaves of tomato could be related to fruit set failure at high temperature. The results show that physiological responses to heat stress at the seedling stage correspond with the responses at the anthesis stage, demonstrating that screening for heat stress sensitivity can be carried out in young plants.     

铝胁迫对柑橘实生幼苗生长的影响

每天用含0、0.2、0.6、1.0和1.6 mmol/L AlCl3•6H2O的1/4 Hoagland营养液浇沙培茶枝柑(Citrus reticulata)、芦柑(C. reticulata)、福橘(C. reticulata)、四川红橘(C. reticulata)、文旦柚(C. grandis)、尤力克柠檬(C. limon)、雪柑(C. sinensis)、酸橙(C. aurantium) (来自湖北)、枸头橙(C. aurantium) (来自浙江)、红木黎檬(C. limonia)、枳壳(Poncirus trifoliata)和枳柚（P. trifoliata × C. grandis）等12个柑橘种类品种实生幼苗3个月。结果表明：雪柑、茶枝柑、芦柑、福橘、四川红橘、尤力克柠檬和枳的耐铝性较强,即使在最高铝（1.6 mmol/L）处理下,其根系、地上部和单株干重均与对照无显著差异;枸头橙、酸橙、红木黎檬和枳柚的耐铝性较差,在最高铝（1.6 mmol/L）处理时,其根系和/或地上部的生长均会受到不同程度的抑制;文旦柚耐铝性最差,最低铝浓度（0.2 mmol/L）处理时,其根系和单株生长量就显著下降。铝胁迫引起茶枝柑、福橘、四川红橘、酸橙和枳实生苗根冠比增加,但对芦柑、枸头橙、尤力克柠檬、红木黎檬、文旦柚和枳柚实生苗根冠比无显著影响;除最低铝处理时雪柑根冠比降低外,其它处理之间无显著差异。     

Aluminium tolerance in lentil (Lens culinaris Medik.) with monogenic inheritance pattern

The objectives of this study were to determine genetics of Al tolerance and whether the Al tolerance observed is governed by the same gene. The lines ‘L‐7903’ and ‘L‐4602’ have been developed through breeding programme as Al‐tolerant lines. These lines showed maximum root regrowth and minimum accumulation of Al and callose as compared to sensitive genotypes (‘BM‐4’ and ‘L‐4147’). Al tolerance in the parents, F₁, F₂ and backcross generations was estimated using the regrowth of the primary root after staining and scoring of fluorescent signals. The F₁ hybrids responded similarly to the tolerant parents, indicating dominance of Al tolerance over sensitivity. The segregation ratios obtained for Al tolerance and sensitivity in the F₂ and backcross generations were 3 : 1 and 1 : 1, respectively. Test of allelism confirmed the same gene was conferring Al tolerance in both genotypes (‘L‐7903’ and ‘L‐4602’) as the F₁ was also tolerant and no segregation of tolerant : sensitive was recorded. These results indicated that Al tolerance is a monogenic dominant trait that can be easily transferred to agronomic bases through backcross breeding technique.     

Marker‐assisted backcross breeding for improvement of drought tolerance in bread wheat (Triticum aestivum L. em Thell)

Drought stress is presently a major productivity limiting factor in wheat. This study developed five wheat lines with inbuilt tolerance to drought stress using marker‐assisted backcross breeding (MABB) approach employing three linked quantitative trait loci (QTLs) in an initial population of 516 BC₁F₁ plants. The high‐yielding wheat cultivar ‘HD2733’ grown over last few years extensively in the eastern plains of India is largely sensitive to drought and is used as the recurrent parent. ‘HI1500’ released for water‐limiting conditions and carrying drought‐tolerant QTLs was used as donor parent. MABB lines were advanced using foreground and background selection, coupled with stringent phenotyping. We identified 29 lines that were homozygous for targeted QTLs in different combinations with background recovery range of 89.2%–95.4%. Further evaluation of selected lines for physiological traits and distinctness, uniformity and stability (DUS) characters under rainfed condition identified five potential varieties for national varietal evaluation programme in the zone. The report is first of its kind in implementing known QTLs for the development of drought‐tolerant wheat lines through MABB approach.     

Combining ability for beet armyworm, Spodoptera exigua, resistance and horticultural traits of selected Lycopersicon pennellii-derived inbred backcross lines of tomato

Ten selected inbred backcross lines (IBL), from a Lycopersicon esculentum cv.‘Peto 84’×Lycopersicon pennellii IBL population, with resistance to beet armyworm (BAW), Spodoptera exigua, higher fruit mass and fruit yield, were crossed with eight elite cultivated L. esculentum inbred lines in a Design II mating design. Three elite inbreds were also crossed to ‘Peto 84′, the IBL recurrent parent, as a control for combining ability. Field plots of all resulting F₁ progenies and control cultivars were inoculated with BAW eggs and evaluated for resistance to BAW, fruit mass, fruit yield, vine size and maturity at three field locations. Reductions in fruit damage by BAW were found in four of the 10 IBL F₁ progenies. Significant male and female general combining ability (GCA) estimates for BAW resistance were observed, but significant specific combining ability for BAW resistance was not detected. The fruit mass of F₁ hybrids was significantly lower than large-fruited controls, but was not significantly different from elite inbred by ‘Peto 95’F₁ hybrids. Selection based on inbred performance identified IBL with positive GCA for BAW resistance and yields in Design II hybrids. BAW resistance in the 09 selected IBL and IBL- derived F₁ progeny was associated with two undesirable traits, later maturity and larger vine size. Index selection of IBL was more effective at identifying IBL with positive GCA for fruit mass and fruit yield than GCA for BAW resistance.     

Development of Gossypium hirsutum lines with cytoplasmic bollworm tolerance from Gossypium arboreum and Gossypium tomentosum

American cotton [Gossypium hirsutum (L.)] grown in India belongs to the race Latifolium. It is prone to bollworms [Helicoverpa armigera (Hubner), Erias vitella (Fabricius), Pectinophora gossypiella (Saunders)] infestation which causes considerable crop loss. Two breeding lines ‘Bikaneri (BN)‐arboreum (ARB)‐16’ and ‘BN‐tomentosum (TOM)‐277’ are cytoplasmic diverse genetic stocks. They were developed by crossing experimental lines ‘Delta Branch Experiment Station (DES)‐ARB16’ and ‘DES‐TOM277’ (non‐recurrent parents) with G. hirsutum‘BN’ (recurrent parent). Compared with BN these stocks possessed higher amount of gossypol, flavonol and phenol contents in leaves, stem and square. Plants were tolerant to bollworms and inherited comparable agronomic properties (yield, boll weight, plant height, number of monopods and sympods and fibre quality). Cotton breeders can use these lines for breeding cotton resistant to bollworm.     

Estimating the pleiotropic effect of the jointless-2 gene on the processing and agronomic traits of tomato by using near-isogenic lines

Two near-isogenic lines of the processing tomato cv. ‘IPA-5’, pheno-typically distinct from each other only in terms of the presence or absence of a jointless fruit pedicel, were used to estimate pleiotropic effects of the recessive gene j-2 on 15 processing and agronomic parameters. Total yield, total yield of mature fruit, total yield of green fruit, total number of fruit, total number of mature fruit, total number of green fruit, mean weight of mature fruit, mean weight of green fruit, mean weight of mature plus green fruit, soluble solids, fruit colour, pH, titratable acidity, sugar: acid ratio, and fruit firmness were compared in jointed (J-2/J-2) and jointless pedicel (J-2/J-2) lines. Statistically significant differences were detected between both isolines for the following parameters: total number of fruit, total yield, total yield of green fruit, and total number of green fruit. In all cases, smaller values were observed in the isoline with the genetic constitution J-2/J-2. These data reinforce the view that they j-2 gene may cause, in some specific tomato backgrounds, significant yield constraints. Furthermore, it was demonstrated that this gene cannot exert any important pleiotropic influence on any of the processing characteristics evaluated.     

Variation and genetics of tolerance to cull fruit formation in slicing cucumber

Cull fruit formation (CFF) in cucumber is a serious problem in subtropical regions. A world collection of cucumber was evaluated in the field for tolerance to CFF over 2 years. Tolerance was identified in landraces collected from the centre of origin (India). Highly significant genotypic effects for tolerance to CFF were observed. The data revealed the presence of genetic variability among cucumber inbreds for tolerance to CFF, which would be useful to develop CFF‐tolerant varieties or hybrids. Genotype‐by‐environment interaction for tolerance to CFF was not detected. Twenty‐one F₁ hybrids evaluated for tolerance to CFF indicated the dominance of a low CFF trait which appears to be controlled by many dominant genes. The in breds ‘JL‐1’, ‘JL‐2’ and ‘JL‐11’ would be good choices as parents for developing CFF‐tolerant cucumber hybrids.     

Inheritance of tolerance to zinc deficiency in barley

Barley (Hordeum vulgare L.) is often grown on alkaline zinc (Zn)‐deficient soils where reductions in yield and grain quality are frequently reported. Currently, the use of Zn‐based fertilizer along with Zn‐deficiency‐tolerant genotypes is considered the most thorough approach for cropping the Zn‐deficient soils; however, developing or breeding genotypes with higher Zn efficiency requires a good understanding of the inheritance of tolerance to Zn deficiency. This study was conducted to determine genetic control of this trait in barley. Two parental cultivars ('Skiff, moderately tolerant; and ‘Forrest’, sensitive), 185 F₂ plants, and 48 F₂‐derived F₃ families from this cross were screened to determine inheritance of tolerance to Zn deficiency using a visual score of deficiency symptoms. The segregation ratios observed indicated that greater tolerance to Zn deficiency in ‘Skiff compared with ‘Forrest’ at the seedling stage is controlled by a single gene with no dominance. The results also indicate that visual scores are useful for genetic analysis of tolerance to Zn deficiency.     

Gamma Ray-Induced Field Tolerance to Phytophthora Blight in Sesame

Due to the non-availability of sources of resistance in Sri Lanka to Phytopbthora blight in sesame (Sesamum indicum) caused by Phytopbthora nicotianae var. parasitica, a mutation breeding programme was initiated. Seeds of three genotypes were subjected to six doses of gamma rays from 100 Gy to 750 Gy from a ⁶⁰Co source. Seeds of M₂ bulks, sampled by variety and treatment from the first five capsules formed on M₁ plants, were grown in a field with a history of repeated incidence of the disease. The best 21 lines, having the highest survival and seed production, identified in the screening of M₃ and M₄ progeny rows of selected M₂ single plants were then tested in a replicated field trial with the recommended cultivar ‘MI 3’ as a control. The plant survival in selected lines averaged 43.3 percent as against 7.2 percent in the recommended variety. Eight selections recorded significantly higher seed yield than ‘MI 3’ at P < 0.01 and another three at P < 0.05. Gamma ray treatments of 450 Gy and 600 Gy produced more lines tolerant to the disease than the other doses used.     

Generating genetic variation in narrow‐leafed lupin (Lupinus angustifolius L.) for plant architecture by ethyl methanesulfonate mutagenesis

Narrow‐leafed lupin (NLL) is a source of protein and fibre with exceptional functional properties useful for a variety of purposes. In adapted NLL germplasm selected for low alkaloid contents, the genetic base is narrow, thus limiting fast breeding progress. In an EMS‐based mutagenesis programme, we have treated 40,000 seeds of cv. ‘Boruta’ and obtained a variety of phenotypic mutant lines expressing novel growth types with altered plant height and/or branching. In 3‐year field trials at two locations, three of these lines exhibited significantly improved grain yield components compared to the cv. ‘Boruta’. Growth types of these promising lines were shown to be inherited in a monogenic recessive manner and should, thus, be easily fixable by breeding.     

Production and characterization of Raphanus sativus-Brassica rapa monosomic chromosome addition lines

Breeding of Raphanus sativus‐Brassica rapa monosomic chromosome addition lines (MALs, 2n = 19) was carried out by backcrossing the synthesized amphidiploid line, Raphanobrassica (R. sativus×B. rapa, 2n = 38, RRAA, line RA89) with R. sativus cv. ‘Shogoin’ (2n = 18, RR). In the first cross of Raphanobrassica× radish, four sesquidiploidal BC₁ plants (2n = 28, RRA, RA89‐36‐1, RA89‐31‐1, RA89‐31‐2, RA89‐31‐3) were successfully developed. In these plants, the chromosome configurations of 9II + 10I and 10II + 8I were observed frequently at first metaphase (MI) of meiosis in pollen mother cells (PMCs). The RA 89‐36‐1 plant produced many seeds in the reciprocal backcrosses with radish. About 50% of the BC₂ plants obtained from the cross of RA89‐36‐1 plant × radish were 2n = 19 plants, followed by 2n = 18 plants (24%) and 2n = 20 plants (19%). In the reciprocal cross, 2n = 19 plants were also developed at the rate of 40%. From analysis of specific morphological traits, 2n = 19 plants were classified into eight types (a‐h). When 25 selected primers were used in polyacrylamide gel electrophoresis, random amplified polymorphic DNA (RAPD) markers derived from B. rapa for each type of MAL were detected in numbers between three for e‐type and 16 for b‐type. RAPD markers specific for each type alone were from one (OPE 05‐344) for h‐type to nine for b‐type. In the g‐type, no marker specific to this type alone was observed. However, 19 bands were common between at least two types. These MAL plants exhibited predominantly the chromosome configuration of 9II + 1I at MI of PMCs, pollen and seed fertility being the same level as the radish cv. ‘Shogoin’. From the morphological traits and DNA markers, eight different MAL types among 10 expected were identified.     

Use of Isozyme-Marked Segments from Wild Barley (Hordeum spontaneum) in Barley Breeding

Fifty-six accessions of Hordeum spontaneum from various Israeli habitats were hybridized with, and their progeny backcrossed three times to H. vulgare cv. ‘Clipper’. Selected chromosome segments marked by one of 24 isozyme loci were transferred to form 84 backcross lines which were nearly isogenic with ‘Clipper’. Each line was made homozygous for a single isozyme-marked segment. These lines were evaluated in preliminary and advanced field trials. The yield, malt extract percentage and grain size of the lines approached or equalled, and sometimes significantly surpassed, that of ‘Clipper’ and more recent commercial cultivars. Three isozyme-marked segments were combined in pairs and the three resultant doubly-marked lines were compared with the reconstituted parental, singly-marked lines and with the ‘Clipper’ recombinant from the same F²-array. The additive effects of single segments on yield or gram size were not significant, whereas half of the six interactions were significant, but in the unfavorable direction. It was concluded that near-isogenic lines can identify segments of wild barley germplasm that are useful for improving yield, but that pairs of these from different habitats may interact unfavourably.     

外源赤霉素浸种对茄子种子萌发和植株生长影响的研究

为研究赤霉素（GA3）对打破茄子种子休眠及植株生长的影响,以16份自交系和2份品种为试材,采用GA3处理种子,对不同自交系种子的休眠特性的解除和杂交品种的植株生长的影响进行研究。结果表明16份自交系取种后1个月芽率都较低,最高为25.5%,最低为0%,不同材料间存在极显著差异,说明初收茄子种子普遍存在休眠现象,但休眠深浅程度存在差异;经1000 mg/L GA3处理,所有自交系的芽率、芽势都有明显提高,其中6份芽率达到90%以上,说明GA3对解除茄子种子休眠效果极为显著。室温干燥器存储4个月后除06036和06039 2份亲缘来自中国北方的黑紫茄自交系芽率在低于80%,其他14份材料均在90%以上。利用GA3浸种处理‘农夫长茄’和‘庆丰紫红茄’对不同生长时期的植株、果实性状和产量调查发现,较高浓度GA3(2000 mg/L)对‘庆丰紫红茄’1叶1心期株高有极显著增加,低浓度GA3浸种处理对‘庆丰紫红茄’及不同浓度GA3对‘农夫长茄’的株高促进作用不明显;4叶期后,不同浓度的GA3浸种处理对‘农夫长茄’和‘庆丰紫红茄’植株高度、茎周径、叶片大小的影响差异均不显著,对2个品种的开花期、商品果性状（单果重、果长、果粗、畸形果率）及产量等影响均未达显著差异;且同一浓度浸种4 h与6 h对植株生长、商品果性状和产量的作用效果一致。本研究可为茄子商用种解除休眠提供理论依据。     

Response of China aster to daylength and gibberellic acid

1. 1.
   Plants of Callistephus chinensis cv. ‘Giant Comet’ were subjected to photoperiods of 8 or 16 hours. In short day (SD) a much greater number of leaves was formed than in long day (LD) before the terminal inflorescence was initiated. By transferring plants from LD to SD at weekly intervals it was established that in LD floral induction is completed about 6 weeks after sowing.