Emerging multi-pathogen disease caused by <Emphasis Type="Italic">Didymella bryoniae</Emphasis> and pathogenic bacteria on Styrian oil pumpkin

The Styrian oil pumpkin, Cucurbita pepo L. subsp. pepo var. styriaca Greb. is a crop of cultural, commercial, and medical importance. In the last decade, yield losses of pumpkins increased dramatically. The ascomycetous fungus Didymella bryoniae (Fuckel) Rehm was identified as main causal agent provoking gummy stem blight as well as black rot of pumpkins. We observed a remarkable phenotypic diversity of the fungal pathogen, which contrasted with a high genotypic similarity. Evidence of pathogenictiy of D. bryoniae on Styrian oil pumpkin was demonstrated in a newly developed greenhouse assay. Isolates representing the five observed phenotypic groups fulfilled the Koch’s postulates. In the field, the fungal disease was often associated with bacterial colonization by Pectobacterium carotovorum, Pseudomonas viridiflava, Pseudomonas syringae and Xanthomonas cucurbitae. The pathogenic behaviour of bacterial isolates on pumpkin was confirmed in the greenhouse assay. The high co-incidence of fungal and bacterial disease suggests mutualistic effects in pathogenesis. With a new assay, we found that bacteria can use the mycelium of D. bryoniae for translocation. We argue that the rapid rise of the multi-pathogen disease of pumpkins results from combined action of versatile pathogenic bacteria and the rapid translocation on a structurally versatile mycelium of the fungal pathogen.     

<Emphasis Type="Italic">In vivo</Emphasis> evaluation of essential oils and biocontrol agents combined with heat treatments on basil cv Genovese Gigante seeds against <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">basilici</Emphasis>

Seed treatments with essential oils (from savory and thyme) and biocontrol agents (Pseudomonas spp. and Fusarium oxysporum) have been evaluated in vivo after dry hot air treatments against Fusarium oxysporum f. sp. basilici on basil seeds. The savory and thyme essential oils showed a significant pathogen control activity because of their innate antifungal activity and because of the seed application method, but the dry hot pre-treatment did not show any obvious effect on the performance of the essential oil treatments. The dry heat treatment improved the Pseudomonas seed dressing effect against F.oxysporum f. sp. basilici, and showed important reductions in plant infection and the disease index on the treated seed plants, without any negative effect on seed germination. However, the pathogen control provided by the heat treatments combined with the application of the biocontrol agents never reached the same performance as the chemical treatments considered as the reference. Thus, short dry heat treatments on basil seeds have been shown to be a valid but complementary seed disinfection method against Fusarium wilt.     

Seed germination of the invasive species Piper aduncum as influenced by high temperature and water stress

Piper aduncum is a common woody weed throughout the tropics and a successful invader in many areas. As this species most often dominates roadsides and forest margins, and these habitats frequently experience extreme changes in temperature and water availability, it is important to understand how the seeds adapt to these stresses. This study investigated the effect of high temperatures and water stress, continuous, periodic or transient, on P. aduncum seed germination before or after imbibition. It was found that P. aduncum seeds exhibited only intermediate tolerance and did not germinate at temperatures above 35°C or water potentials below ?0.6 MPa. However, this species is well adapted to local conditions, with fruit ripening in the rainy season, seed desiccation tolerance to eRH 8%, rapid germination under wet conditions, higher temperature tolerance than the maximum ground temperature, germination of most seeds after 60 h continuous heat treatment or daily periodic heat treatments up to 5 h at 40°C and insensitivity to 12 h heat treatment at 40°C during the whole germination process. The intermediate tolerance to high temperature and water stress of P. aduncum, in combination with local environmental conditions in Xishuangbanna, makes P. aduncum an intermediate invader in this area.     

The effect of chemical and heat treatments on germination of Commelina benghalensis L. aerial seeds

The effects of concentrated sulphuric acid, dry heat, hot water and NaOCl treatments on the germinability of dormant large and small aerial Commelina benghalensis L. seeds were evaluated. Concentrated sulphuric acid and NaOCl treatments were more effective than the dry heat and hot water treatments in breaking the dormancy of C. benghalensis aerial seeds. Treatments increased germination of both seed types due to its effect on the seed coat integrity. A scanning electron microscope revealed that changes as a result of scarification occurred in the hilum region of the seed and in the seed coat surface. The large aerial seeds were affected by all treatments more than the small aerial seeds. Difference in germinability between the two seed types was related to the difference in their seed vigour.     

Production,size, and germination of broad‐leaved dock seeds collected from mother plants grown under different nitrogen,phosphorus, and potassium supplies

Rumex obtusifolius is believed to be a nitrophilous weedy species that spreads mainly by seed. However, the effects of nutrient availability on seed production never have been investigated. In this study, how the amount of seed production per plant, the chemical composition of the seeds, and their size and germination are affected by the supply of N, P, and K was investigated. A pot fertilizer experiment with 10 treatments (combinations of 0, 150 [N1], and 300 [N2] kg N ha^?1, 0, 40 [P1], and 80 [P2] kg P ha^?1, and 0 and 100 [K] kg K ha^?1 applied twice per vegetation season) was carried out in Prague, Czech Republic, in 2008 and 2009. The seeds from plants that were cultivated since the spring were collected each August. The germination of the seeds was determined in long‐daylight conditions at a stable temperature of 20°C. The number of seeds per plant ranged from 0 in the P1 and P2 treatments and <200 in the control and K treatments to almost 9000 in the N2P2K treatment. The number of seeds per plant was positively correlated with the number of stems per plant and the number of seeds per stem. The relationship between the amount of seeds per plant and the individual seed weight was positive. The concentration of N, P, and K in the seeds was affected by the treatments. The weight of 1000 seeds ranged from 1.3 to 1.7 g. The seed length ranged from 2.11 to 2.34 mm and the seed width varied from 1.26 to 1.42 mm. With the exception of the control (with 94% germination), the amount of seed germination was >98% in all the other treatments in 2008. In 2009, the amount of seed germination was >95% in all the treatments, except N1 and N2, where 93% and 89% germination, respectively, was recorded. The germination rate was positively related to the P concentration in the seeds. The amount of time that was necessary for 50% seed germination ranged from 1.53 to 2.89 days and was not related to the N concentration in the seeds, but it was negatively related to the P and K concentrations. A balanced N, P, and K supply to the mother plant strongly affected the number of produced seeds and their chemical composition and germination ability.     

Seed germination, seedling establishment and growth patterns of wrinklegrass (Ischaemum rugosum Salisb.)

Several laboratory and glasshouse experiments were conducted to assess seed germination, seedling establishment and growth patterns of wrinklegrass (Ischaemum rugosum Salisb.) influenced by temperature and light regimes, and chemical media. Wrinklegrass was a positively photoblastic species, and seed germination was temperature‐dependent and light‐mediated. Seeds soaked in distilled water for 24 h, or oven‐dried at the respective temperature regimes of 15, 20, 25, 30, 35, or 40°C prior to treatment in distilled water and incubated in darkness, failed to germinate. Likewise, no germination prevailed when the seeds were exposed to similar temperature regimes and treated with 0.2 m KNO₃, 5% H₂O₂ or 0.01 m HNO₃, and incubated under continuous darkness. Seeds treated with 5% H₂O₂ at 30°C, or oven‐dried and treated with 0.01% M HNO₃ at 35°C registered 10 and 20% germination. Approximately 75 and 90% of the light‐exposed seeds for all treatments germinated in the first three and six days at 25°C. No germination occurred at 15°C in the first three days after treatment. Seeds subjected to 40°C for six days after treatment recorded 36% germination. The optimum temperatures for seed germination were 25–30°C. Seed drying and soaking treatments widened the windows of the optimal temperatures for wrinklegrass germination. The acidic media of KNO₃, H₂O₂ or HNO₃ favored seed germination. Less than 5% of seed germination occurred with burial or water inundation at depths exceeding 2 cm. Seed burial or inundation at ≥2 cm depths inhibited seed germination. Seeds sown onto moist paddy soils registered ca. 50% germination. Free‐floating seeds on the water surface registered ca. 98% germination within the first six days after seeding. The mean number of seedlings that survived was inversely proportional to water depths, with close to 100% mortality at the 14 cm depths of inundation. Both plant height and seedling survival were linearly proportional to the amount of root mass of seedlings which penetrated the soil. The weed was a prolific seed producer (ca. 6000 seeds/genet or 18 000 seeds/genet per year). The vegetative and reproductive efforts of each wrinklegrass plant registered values of 0.68 and 0.32, respectively.     

Implications of bacterial contaminated seed lots and endophytic colonization by Pseudomonas fuscovaginae on rice establishment

The economic impact of seedborne bacterial diseases on rice production provides a major motivation for research on seed health. This paper reports on the endophytic growth of a rifampicin‐marked strain of the seedborne rice pathogen Pseudomonas fuscovaginae. The bacterium was found in most tested seeds indicating that, even without visible discolouration, seed transmission is possible. Crushed discoloured seeds contained more bacterial cells than did non‐crushed discoloured seeds. These bacteria were released during seed soaking, contaminating clean seed and lowering seed germination. Cells of a rifampicin‐resistant strain of P. fuscovaginae, which had been inoculated onto rice seeds, were subsequently recovered from different growth stages and from different rice tissues, thereby indicating endophytic colonization. These results have implications for seedling establishment, as symptomless seeds do not assure disease‐free seeds, and the presence of seedborne bacteria results in poor germination and poor seedling establishment. Elimination of seedborne bacteria by soaking in sodium hypochlorite can increase seed germination. This could be used in developing control strategies, and, if practised regularly, reduce entry of seedborne disease‐causing organisms into crops, resulting in lower disease pressure.     

Effects of some chemical factors,prechilling treatments and interactions on the seed dormancy‐breaking of two Papaver species

Seed dormancy is a common strategy of many plants to survive in natural and agricultural ecosystems. This study examined the effects of some chemical factors, including gibberellic acid and potassium nitrate, the prechilling temperature, duration and conditions and the light regimes on the seed dormancy‐breaking of Papaver rhoeas L. and Papaver dubium L. The results showed that all the tested seed dormancy‐breaking treatments significantly stimulated the germination of the two Papaver species. The seed germination was significantly influenced in relation to the seeds that were treated with 0–1250 p.p.m. of gibberellic acid. The maximum germination was observed in P. rhoeas L. at 750 p.p.m. and in Pa. dubium L. at 500 p.p.m. in the light/dark regime. There was a significant increase in the germination with an increase in the potassium nitrate concentration. The greatest germination was achieved at the lowest potassium nitrate concentration (0.5 g L^?1) in the light/dark regime. The wet prechilling was more effective than the dry prechilling in the dormancy‐breaking of both P. rhoeas L. and Pa. dubium L. The highest germination percentage was found in the wet prechilling condition after 45 days' prechilling duration. The combination of gibberellic acid and potassium nitrate was more successful than their separate application in the stimulation of germination in both Papaver species. Among the combined treatments of prechilling and gibberellic acid, the highest germination of P. rhoeas L. was recorded in the seeds that were treated with wet prechilling for 45 days with 750 p.p.m. gibberellic acid, while in Pa. dubium L., the maximum germination was recorded with wet prechilling for 45 days with 500 p.p.m. of gibberellic acid.     

Reduction of pesticide hazards to wild life: An appraisal of experience gained in Britain 1960 - 67

Abstract

The plant oils groundnut, coconut, mustard, sesame, soybean and rapeseed used as surface protectants at 1, 3 and 5 ml/kg of seed to test their efficacy against C. chinensis on a variety of chickpea resulted in significantly less oviposition on treated than untreated seeds. Least oviposition (34.3 eggs) occurred on seeds treated with mustard oil at 5 ml/kg, less with coconut oil at 5 ml/kg (46.0 eggs) and 3 ml/kg (47.3 eggs). Minimum percentage adult emergence (0.5) occurred from mustard oil‐treated seeds at 5 and 3 ml/kg, followed by groudnut (7.6), soybean (16.7) and rapeseed (6.2) oils used at 1 ml/kg. All the test oils adversely effected hatching and development of embryos, resulting in further population suppression. Seeds showed only 0.5% damage when treated with mustard oil at the rate of 5 and 3 ml/kg, and rapeseed at 5 ml/kg. Oil treatments did not adversely effect seed germination.     

外源硫化氢对加工番茄种子耐盐性及抗氧化酶的影响

为明确硫化氢对盐胁迫下加工番茄种子萌发的缓解作用,用Na Cl半致死浓度为85 mmol·L~(-1)的KT-63(耐盐性弱)和半致死浓度为120 mmol·L~(-1)的KT-18(耐盐性强)为材料,用各自的半致死浓度与不同浓度的NaHS(0.2,0.4,0.6,1.0 mmol·L~(-1))分别配成混合液处理种子。结果表明,随着NaHS浓度的增加,种子的发芽率、发芽势、发芽指数、活力指数、SOD、POD、CAT活性呈先上升后下降的趋势,其中与盐胁迫单独处理相比,用0.4mmol·L~(-1)NaHS处理,种子的发芽率、发芽势、发芽指数、活力指数、SOD、POD、CAT活性在KT-63中分别提升70%、250%、120%、130%、6.7%、150%和180%,在KT-18中分别提升50%、250%、60%、80%、4.3%、160%和200%,而MDA的含量显著降低,并且对KT-63的缓解效应强于KT-18。综上所述,H2S(0.4 mmol·L~(-1))有效缓解了加工番茄萌发过程中盐胁迫的抑制作用,促进了种子的萌发。     

Seed dormancy and soil seedbank of the invasive weed Chenopodium hybridum in north‐western China

Seed dormancy and persistence in the soil seedbank play a key role in timing of germination and seedling emergence of weeds; thus, knowledge of these traits is required for effective weed management. We investigated seed dormancy and seed persistence on/in soil of Chenopodium hybridum, an annual invasive weed in north‐western China. Fresh seeds are physiologically dormant. Sulphuric acid scarification, mechanical scarification and cold stratification significantly increased germination percentages, whereas dry storage and treatments with plant growth regulators or nitrate had no effect. Dormancy was alleviated by piercing the seed coat but not the pericarp. Pre‐treatment of seeds collected in 2012 and 2013 with sulphuric acid for 30 min increased germination from 0% to 66% and 62% respectively. Effect of cold stratification on seed germination varied with soil moisture content (MC) and duration of treatment; seeds stratified in soil with 12% MC for 2 months germinated to 39%. Burial duration, burial depth and their interaction had significant effects on seed dormancy and seed viability. Dormancy in fresh seeds was released from October to February, and seeds re‐entered dormancy in April. Seed viability decreased with time for seeds on the soil surface and for those buried at a depth of 5 cm, and 39% and 10%, respectively, were viable after 22 months. Thus, C. hybridum can form at least a short‐lived persistent soil seedbank.     

两种雀麦种子萌发期耐热性比较研究

设置了八个变温梯度 ,三种播前预措方式及一个对照 ,分别对两种雀麦 (沙地雀麦Bromus ircutensis和无芒雀麦 Bromusinermis)种子进行萌发测试。测定了不同处理下的发芽率、发芽指数、休眠率和死亡率 ,并依此比较了这两种牧草种子在萌发期的耐热性能。结果表明 ,从发芽率和发芽指数看 ,二者并无明显的差异 ( P<0 .0 5) ,在较低的温度下二者都有较高的发芽率和发芽指数 ,当温度超过 45℃时二者都不萌发。从休眠和死亡状况可知 ,沙地雀麦种子比无芒雀麦种子有较强的耐高温性。三种预措方式中 ,三次回干效果较好     

Health of farmer-saved maize seed in north-east Nigeria

Many Nigerian farmers depend for their seed on seed-producing farmers, the so-called informal Seed System (SS), but seed quality of the SS is unknown. Farmers planting low quality seed risk poor field emergence and low plant vigour as a result of low physiological quality or infection with seed-borne pathogens. The objective of this research was to test seed quality of maize seed from the informal SS in north-east Nigeria. A total of 46,500 seeds (93 samples of 500 seeds each) were tested for germination, off-types and seed health. Seed pathology was quantified by plating disinfected seeds onto agar, and identifying the fungi present after 3 days incubation. Twelve seed-borne pathogens were identified including Bipolaris maydis (found in 45 % of the farmer-produced samples), Botryodiplodia theobromae (97 %) and Curvularia lunata (38 %). All samples were infected with Fusarium verticillioides, with a median infection incidence of 59 % (2009) and 51 % (2010). None of the 93 samples tested passed the demands for certified seed of the National Agricultural Seeds Council (NASC) in Nigeria, in particular the maximum limit of five off-types per kg seed sample. Based on these results, seed-producing farmers must improve the health of seed. The NASC should revise the standards for off-type seeds to minimize the time spent by farmers sorting planting material.     

<Emphasis Type="Italic">Aphelenchoides gorganensis</Emphasis> n. sp. (Nematoda: Aphelenchoididae)<Emphasis Type="Italic">,</Emphasis> a new species from Iran

Phytophthora capsici infection of chili pepper seedlings can cause substantial losses due to damping-off and collar rot diseases. Chemical control is no longer effective due to reported resistance development, on top of the related environmental concerns and the consumer demands for reduced use of fungicides. Biological control is a sustainable option, with several agents having been reported to be effective against this pathogen. This research focused on optimizing the application of strain THSW13 of Trichoderma hamatum and a bacterial isolate BJ10–86 with the objectives of improving chili pepper seed germination, reduce damping-off disease incidence, and improve the growth of the seedlings. Bacterial isolate BJ10–86 was subjected to molecular identification and found to be Pseudomonas aeruginosa. Chili pepper seeds treated with the biocontrol agents, individually or in combination, were seeded into commercial nursery media that had been pre-inoculated with P. capsici zoospores. Over a period of 35 days the chili pepper seed treatments significantly (P = 0.008) reduced the disease incidence of seedlings damping-off. Combined application of T. hamatum and P. aeruginosa was the best biocontrol treatment with an area under disease curve of only 36.61 units compared to 92.87 units for the control treatment. Similar results were observed in vitro where T. hamatum and P. aeruginosa synergistically inhibited P. capsici growth by 73.2 %. The inhibition activity of this treatment was similar to mefenoxam treatment, which implies that it is an effective and sustainable alternative for chili pepper seed treatment. The biocontrol seed treatment had no effect on seed germination and seedling growth.     

Effects of the seed weight and burial depth on the seed behavior of common ragweed (Ambrosia artemisiifolia)

Common ragweed (Ambrosia artemisiifolia L.) is one of the annual plants that were described recently as invasive weeds in Europe. This species is described as an invasive plant that produces seeds that are highly variable. Its production of variably sized seeds is regarded as promoting its spread in different environments. Experiments were carried out to determine the influence of the seed weight and temperature on germination and the influence of the seed weight and burial depth on seedling emergence. The seeds were divided into a number of classes of weight and the seed weight effect on germination was evaluated by Petri dish assays. In another experiment, the seeds were buried at different depths in a clay soil/sand mix to estimate the burial effect on germination and seedling emergence. The germination level of A. artemisiifolia was high overall, between 76.8% and 94.2%. The seed germination was modified by temperature but it was not influenced by the seed weight. The amounts of germination and seedling emergence were greater for the seeds on the soil surface and decreased with an increasing burial depth, from 2 to 8 cm. No germination or emergence was observed for the seeds that were buried at 10 and 12 cm. The lightest seeds were more sensitive to burial. A greater level of seedling emergence for those seeds that were placed near the soil surface could explain the success of this species in open habitats, where the probability of deeper burial is low. After high seed production, the management of A. artemisiifolia in fields could be partly achieved through soil tillage, burying seeds below 10 cm, and not carrying out deep soil tillage the following year.     

Germination of Setaria chevalieri caryopses

Germination studies were made on Setaria chevalieri caryopses (seeds). The seeds imbibed readily upon moist incubation. An after-ripening period which followed a cyclic patlern was necessary for maximum germination. Freshly harvested seed germinated in the presence of light, but only very sporadically in the dark. The germination of dark incubated seed was improved if the seeds were subsequently exposed to light. This photodormancy became less pronounced with dry storage. Treatment with red light increased germination. but was reversed by far-red light suggesting that a phytochrome system operates in the seeds. Sodium azide treatments did not stimulate germination in the dark but were effective in the presence of light.     

Paraquat tolerant Lolium perenne L.: effects of paraquat on germinating seedlings

A cultivar of Lolium perenne L. (Causeway) selected for tolerance to foliar-applied paraquat was shown also to be tolerant at seed germination and establishment. When seeds were germinated in paraquat solutions (1, 3, 9, 27 ppm), Causeway was more than ten times as tolerant as a normal cultivar of L. perenne. When germination and survival were studied in a soil which had been sprayed with paraquat (0.0, 0.3, 0.9, 2.7 kg/ha) before sowing, Causeway was nearly three times as tolerant as a normal cultivar. Holcus lanatus L. was about equal to normal L. perenne, but Poa trivialis L. was less tolerant. Phytotoxicity was greater in a 10.5% organic than a 4.8% organic soil. It is concluded that the mechanism of paraquat tolerance operates in the non-photosynthetic tissues of germinating seedlings as well as in the photosynthetic tissues of older plants, although the degree of tolerance varies according to the mode and stage of application of the herbicide. There might be advantages in using a paraquat tolerant cultivar of L. perenne when direct drilling grass after sward destruction by paraquat.     

Influence of Root Exudates on Orobanche Seed Germination*

Broomrape (Orobanche ramosa L.) is a common root parasite of solanaceous, leguminous and other crops grown in the semi-arid regions of the world. The seeds germinate when root exudates from host plants are released in their immediate vicinity (Lindley, 1853; Koch, 1887; Chabrolin, 1934). Brown et al. (1951a) reported that non-host plants, such as flax (Linum usitatissimum L.) may stimulate Orobanche seed germination without being parasitized. The stimulating properties of flax exudate were studied by Brown et al. (1951b). They reported that the stimulant was unstable in alkaline solutions, but moderately stable in weakly acidic media, which may indicate the presence of an acidic (lactone) grouping. Nash & Wilhelm (1960) reported that gibberellic acid in agar media stimulated O. ramosa seed germination. Abu- Shakra, Miah & Saghir (1970) found that pre-treatment of 0. ramosa seeds with 100 ppm of gibberellic acid followed by incubation on a flax-root diffusate agar medium gave a high (81·7%) germination. The purpose of this study was to collect root exudates from three species of plants cultured under three experimental systems, namely (a) germ-free, (b) glasshouse (non-sterile), and (c) growth chamber (hydroponic, initially aseptic), and to evaluate their biological activity as germination stimulants for O. ramosa seeds. The plants used were tomato (Lycopersicon esculentum Mill.), sorghum (Sorghum vulgare Pers.) and flax. Exudate from marigold (Tagetes erecta L.) also was collected from germ-free culture.     

鲜食玉米种子包衣对地下害虫的防控以及苗期生长发育的影响

为研究3种种衣剂对鲜食玉米主要地下害虫的防治效果以及对幼苗生长发育的影响，从而筛选出高效低毒的种衣剂。试验以京科甜183和京科糯2010为试验品种，比较了3.5%满适金＋30%锐胜、福亮（40%溴酰·噻虫嗪种子处理悬浮剂）和50亿孢子/g球孢白僵菌3种种衣剂的室内和田间试验结果。结果表明：各药剂处理对鲜食玉米均不产生药害，出苗安全，没有发现药害植株。种子包衣可提高种子活力和出苗率，其中在3.5%满适金＋30%锐胜处理下，京科甜183的发芽势和发芽率最高，分别达到91.5%和92.75%；京科糯2010在50亿/g球孢白僵菌的处理下发芽率达到最高，为93.00%，发芽势在3.5%满适金＋30%锐胜处理下达到最高，为91.50%。3种种衣剂都能促进幼苗的株高和干物质的积累。对于地下害虫的防治效果，其中50亿孢子/g球孢白僵菌对地下害虫的防治效果最好，对京科甜183和京科糯2010的地下害虫的防治效果达到79.67%和88.67%。为了既能促进植株生长发育又能很好的防治地下害虫，生产中推荐球孢白僵菌与低毒种衣剂菌药混用。     

Biology of Commelina benghalensis L. in south-eastern Queensland. 2. Seed dormancy, germination and emergence

Germination of freshly harvested seeds of Commelina benghalensis L. varied from 0–3% for small aerial seeds, 20–35% for large aerial seeds and from 33% for small underground seeds to 90% for large underground seeds. Innate dormancy of all seed types was completely overcome by clipping the seed coat. Exposure to 90°C dry heat for 2 h was also effective in increasing germination of the three strongly dormant seed types. Optimum temperature for germination varied with the different seed types. Periods of likely major weed infestation from the four seed types were predicted using soil temperature data. Exposure to light increased germination but was not essential and underground seeds responded more to light than aerial seeds. Optimum depth of emergence for the four seed types was from 0 to 50 mm and there was a positive correlation between maximum depth of emergence and seed weight.