Low Seedling Vigor Research Articles

A point mutation in VIG1 boosts development and chilling tolerance in rice

The rice paddy-direct seeding system has been widely adopted due to its low cost and convenience, whereas its application is mainly constrained by low seedling vigor, cold sensitivity, eventually resulting in reduced grain yield. Here, we show vig1a and vig1b, two allelic mutants of OsbZIP01, that both demonstrate greatly enhanced seedling vigor and chilling tolerance but differ in final grain production. The vig1a phenotype can be obtained via simultaneous mutation of the genes OsbZIP01 and OsbZIP18, or by selectively manipulating the basic region of OsbZIP01. Destroying the leucine zipper region of OsbZIP01 in vig1a turns vig1a to be vig1b. Further analysis reveals that OsbZIP01 and OsbZIP18 function cooperatively in diverse crucial biological programs that determine seedling establishment, chilling tolerance, and grain yield through their interactions. These findings provide a strategy toward simultaneously improving seedling vigor, chilling tolerance, and grain yield for rice production.

Identification of Drought Tolerant Chickpea Genotypes under Simulated Drought

Chickpea (Cicer arietinum L.) is one of the most important legume crops worldwide, with high protein content. Chickpea productivity is highly threatened by abiotic stresses, of which drought exerts the most crucial role in terms of growth inhibition and yield losses encountered. Since germination is a critical stage that is negatively affected by drought, an experiment was conducted to estimate the genotypic variability among 27 chickpea genotypes and to determine the seed germination and seedling growth ability under water stress conditions. Seeds were subjected to water stress by using polyethylene glycol (PEG-6000) at five stress levels (0, 5, 10, 15 and 20 % PEG). Among the genotype DIBG 205 (94.50%) recorded highest germination percentage compared to other genotypes. Root length recorded was highest in ICCV 4958 (18.48 cm) under 10% PEG -6000 and decreased with increase in osmotic stress. Drought significantly affected germination as well as all other associated traits with the effects of stress being analogous to the stress level applied. Seedling vigour index is a suitable selection criterion for drought tolerance, high seedling vigour index was observed in DIBG 205 and ICCV 4958 showing increased drought tolerance at high stress level, whereas low seedling vigour index was recorded in ICCV 201217 and ICCV 201116 indicating their possible exploitation as valuable genetic material for further breeding programs for drought tolerance.

RESPONSE OF RICE (ORYZA SATIVAL.) GENOTYPES UNDER TO DIFFERENT PLANTING DATES

Rice (Oryza sativa L.) is a vital food crop that holds a significant position in the world's economy. It ranks third globally in terms of production, following wheat and maize. Moreover, rice serves as the staple food crop for approximately two-thirds of the world's population. The planting date has a significant impact on rice productivity. When rice is sown under optimal conditions, including favorable air and soil temperatures and adequate soil moisture, the crop's performance shows a notable improvement. Nonetheless, planting rice too early can expose the crop to cold temperatures, which may result in poor germination, low seedling vigor, and seedling mortality. Conversely, planting too late can lead to reduced yields and grain quality since the critical reproductive phase coincides with the peak of summer heat, negatively affecting rice grain yield and quality. During the Khaif season of 2022, the field experiment was conducted at the Rice Research Center (RRC) Dokri. The experiment was laid out in split plot design containing three sowing dates’ viz. 30thJune, 15thJuly and 30thJuly in main plots and four rice genotypes viz. NUYT-M-11, NUYT-M-8, NUYT-M-10 and Latify (check) as sub plot treatments. Nevertheless, rice crops sown on June 30th demonstrated markedly superior performance compared to other sowing dates. These crops exhibited a plant height of 97.27 cm, 19.18 tillers per plant, a panicle length of 20.11 cm, a seed index of 29.82 g, a biological yield of 8964 kg/ha, a grain yield of 5330 kg/ha, and a harvest index of 84.11%. The interaction between genotypes and sowing dates significantly influenced the observed plant height, tillers per plant, panicle length, seed index, biological yield, grain yield, and harvest index. Among the genotypes, NUYT-M-11 sown on June 30th displayed the highest values for these parameters.

X-radiation of Lotus corniculatus L. seeds improves germination and initial seedling growth

Purpose Lotus corniculatus L. (bird’s foot trefoil, BFT) is a valuable perennial legume forage species due to its high nutritive value, persistence under grazing, and condensed tannin content that improves ruminant production and prevents bloating. However, it is less preferred by farmers compared with other perennial forage legumes such as alfalfa because of slow germination, slow establishment and low seedling vigor. This study was conducted to determine whether X-ray seed priming could improve these deficiencies. Materials and methods Seeds of L. corniculatus cv. ‘AC Langille’ were irradiated at 0, 100, and 300 Gy. Non-irradiated and irradiated seeds were sown on Murashige and Skoog/Gamborg medium under in vitro conditions and cultured for 21 days. Germination percentage, mean germination time (MGT), germination rate index, length of shoot and root, fresh and dry weight of shoot and root, dry matter ratios of shoot and root, water content of shoot and root, and seedling vigor index were measured. Results The results of this study demonstrated that X-ray seed priming significantly increased the germination percentage of L. corniculatus, increased the germination rate and thereby shortened the MGT, and improved seedling growth. However, X-ray pretreatment also decreased seedling shoot and root biomass. Conclusions In this study, it is reported for the first time that X-ray seed pretreatment has the potential to address important seedling establishment issues in L. corniculatus.

Changes on Sugar and Starch Contents during Seed Development of Synergistic Sweet Corn and Implication on Seed Quality

Synergistic sweet corn equipped with multiple-recessive genes encoding sugar synthesis is proposed through hybrid breeding to improve the balance eating quality including flavor, texture, and aroma. However, the drawback on seed quality occurs such as low germination and poor seedling vigor. This study aimed to investigate the changes of carbohydrate contents on seed quality of five sweet corn genotypes differing in the number of equipped recessive genes during seed development. Seeds were sampled at 4-day intervals from 18 to 46 days after pollination (DAP) and analyzed for seed germination, sugar, water-soluble polysaccharide, and starch. Then, their relationships were analyzed by using time series regression analysis. Although there were significant differences among 5 corn genotypes in their seed germination and carbohydrate contents, some genotypes showed responses in similar patterns. The optimal time to harvest seeds was genotype-dependent, which were 38 DAP for triple-recessive gene (btbtsh2sh2wxwx) and single-recessive genes (BtBtsh2sh2WxWx and Sh2Sh2susuWxWx) and 42 DAP for double-recessive genes (BtBtsh2sh2wxwx). The regression analysis revealed that seed germinability could be predicted by total starch content in synergistic sweet corn lines during seed development stages; however, this prediction seemed to be negligible in sweet corn genotypes equipped with a single-recessive gene. Implications and further suggestions for establishing an effective seed production technique and seed quality of synergistic sweet corn are discussed.

<p><strong>Seedling vigour as a potential indicator for rapid screening of rice (<em>Oryza sativa </em>L.) genotypes for aluminium (Al) toxicity tolerance</strong></p>

Aluminium (Al) is solubilized into a phytotoxic form [Al(H2O)63+] in acid soil, which is known as Al3+. Al toxicity is the primary growth-limiting factor for plants in acid soils. Breeding of rice for enhanced Al tolerance considered to be an important approach for increasing grain yield in acid soils. In the present endeavour, we studied the effects of toxic levels of Al on vigour of rice seedlings under hydroponics and finally grouped the genotypes with varied degree of tolerance to Al toxicity based on vigour index. Good seed germination (%), high speed of germination and high vigour index indicate uniform crop stand. Germination ranged from 72-99.50%. It was significantly high for almost all genotypes (³80%) except three. The speed of germination ranged from 9.75 to 29.99 in control. Most of the genotypes showed high speed of germination (>15.00) except a few. Remarkable reduction in seedling vigour has been reported earlier under stressed environments. Low seedling vigour has been identified as the key factor responsible for poor germination and uneven seedling establishment. Based on the vigour index, nine genotypes were classified as tolerant, 19 as moderately tolerant and 12 as susceptible. Among the tolerant genotypes, UBKVR-3 showed maximum value for vigour index followed by UBKVR 19, UBKVR 9, UBKVR 8, Parijat, MTU 1075 and Radhunipagal. Most susceptible genotypes based on seedling vigour were found to be Pusa Basmati, Aiswarya and Pratikha. It is to be mentioned that till now there is no clear and distinct divisions of vigour index for classification into different levels of tolerance towards Al toxicity. In our study, we have identified distinct classes for grouping of genotypes endowed with different levels of tolerance. The values of the vigour index depend upon root length, shoot length or some other characters used for calculation of vigour index. The magnitude of the vigour index may not be useful for classification uniformly across the crops as well as genotypes within the crop. Hence, the procedure used in this work may overcome the above mentioned constraints.

Development of Tetrazolium Test as Vigor Analysis Method of True Seed of Shallot

Uji tetrazolium (TZ) merupakan salah satu metode untuk mengestimasi viabilitas dan vigor benih. Penelitian ini bertujuan untuk memperbaiki metode analisis vigor pada benih botani bawang merah. Pada penelitian ini digunakan dua varietas benih bawang merah, yaitu Trisula dan Tuk-tuk. Pre-treatment dalam uji tetrazolium benih bawang merah dilakukan dengan perendaman benih dalam air selama 18 jam. Sebelum pewarnaan benih disiapkan dengan menggores sisi lurus secara longitudinal sebagai satu-satunya irisan tipis, dan sisi cembung benih ditusuk dengan scalpel. Benih diwarnai selama 18 jam dalam larutan tetrazolium pada suhu 1% suhu 30 oC dalam kondisi gelap. Pola pewarnaan benih diklasifikasikan dalam empat kategori yaitu empat pola normal kuat sebagai kriteria benih vigor, lima pola normal lemah, tujuh pola abnormal, dan empat pola benih mati. Parameter fisiologis viabilitas dan vigor berkorelasi erat dengan hasil pola vigor/ normal kuat. Pola normal kuat memiliki koefisien korelasi (r) yang tinggi dengan parameter uji fisiologis di laboratorium termasuk indeks vigor (r= 0.882), bobot kering kecambah normal (r= 0.899), dan kecepatan tumbuh (r= 0.875). Hal ini mengindikasikan pola pewarnaan vigor dapat memprediksi vigor benih.

Upland Cotton (Gossypium hirsutum L.) Fuzzy-Seed Counting by Image Analysis

In recent years cottonseed size has been reduced as a result of the substantial fiber yield increases cotton breeders have made. Small cottonseed size has been associated with reduced germination, low seedling vigor and stand establishment, and has created production problems for downstream whole seed users. The potential loss in revenue to the cotton industry due to small seed size is substantial and has prompted a renewed effort by breeders to generate high-yielding, high-quality varieties with increased seed size. To aid these efforts and enable a better understanding of the effects of seed characteristics on fiber, a fuzzy-seed imaging method was developed. The method utilizes inexpensive, off-the-shelf equipment and an open source image processing pipeline to derive the number of seeds, seed index, and seed area, height, width, and perimeter. The time to image the seed and process the image takes less than three minutes per sample on average. The seed counts and seed index were strongly correlated with manual measurements at r = 0.967 and 0.693, respectively. Associations among seed characteristics and fiber indicate seed area, when used to calculate lint density, could be a useful selection criterion for breeders to increase both yield and seed size.

DURAÇÃO DA FASE DE MUDAS EM EUCALIPTO SIMULADA EM CENÁRIOS DE AUMENTO DE TEMPERATURA

A mudança climática é um tema atual em debates científicos e de interesse na área florestal, porém, estudos da vulnerabilidade de espécies florestais cultivadas às mudanças climáticas são escassos. O objetivo deste trabalho foi simular a duração da fase de mudas de duas espécies de eucalipto (Eucalyptus saligna e Eucalyptus grandis) em cenários de aumento de temperatura do ar em Santa Maria-RS, considerando várias datas de emergência. A fase de mudas foi considerada da emergência das plântulas até o aparecimento da 25ª folha na haste principal. A taxa de aparecimento de folhas diária (TAF) foi estimada através de um modelo multiplicativo com uma função de resposta não linear da TAF à temperatura média do ar, com coeficientes para as espécies Eucalyptus saligna e Eucalyptus grandis. Foram considerados doze datas de emergência (dia 15 de cada mês do ano) e seis cenários climáticos (atual, +1°C, +2°C, +3°C, + 4°C, +5°C). Os cenários climáticos constituem-se séries sintéticas de cem anos de dados de temperatura mínima e máxima diária do ar. Em cada um dos anos dos cenários climáticos e em cada data de emergência, o modelo de TAF para cada espécie foi rodado e contabilizado o número de dias da emergência até o aparecimento da 25ª folha. A análise estatística constou de análise de variância para a variável duração da fase de mudas, considerando um experimento tri-fatorial 6 x 12 x 2 (cenários climáticos x datas de emergência x espécies), em delineamento inteiramente casualizado, sendo cada ano da simulação uma repetição (n=100). Os resultados indicaram uma diminuição na duração da fase de mudas em cenários climáticos mais quentes nas emergências ocorridas de março a setembro, e um aumento na duração nas emergências de outubro a fevereiro e, ao final de um ano, o aumento de temperatura tende a diminuir o tempo de mudas no viveiro e assim aumentar a produção anual de mudas de eucalipto. Benefícios e desvantagens destes resultados devem ser considerados em políticas de mitigação dos efeitos do aquecimento global na silvicultura.

Swarna × Oryza nivara introgression lines: a resource for seedling vigour traits in rice

AbstractSeedling vigour is an important indicator of crop establishment, subsequent crop growth and yield. Initial seedling vigour is most vital in case of water-limited conditions and in environments where the crop is exposed to different stresses at the early growth stage. Wild and weedy species are well known for their vigour and survival in adverse environmental conditions. Seedling vigour traits of backcross introgression lines (BILs) derived from Swarna × Oryza nivara IRGC81848(S) (accession from Uttar Pradesh, India) and IRGC81832 (K) (accession from Bihar, India) were studied in wet (Kharif) and dry (Rabi) seasons. Seedling vigour was estimated in terms of plant height and tiller number at 30 and 60 d after transplanting under field conditions. In both the seasons, 148S showed highest seedling vigour for plant height. The highest number of tillers were produced by 7K in Kharif and 248S in Rabi season. 75S showed the highest percentage increase in tiller number consistently. High yielding BILs 166S, 14S and 148S showed higher seedling vigour indices compared with checks Tulasi and Sahbhagidhan. Seedling vigour was also evaluated using paper roll method and shoot length, root length and dry weight were used to estimate vigour index. Season-wise association studies were conducted to determine the relative contribution of seedling vigour to yield traits. Seedling vigour was significantly correlated with yield traits. Markers RM217 and RM253 on chromosome 6 differentiated lines with high seedling vigour from those with low seedling vigour and have the potential for use in marker-assisted breeding.

Viability and Dormancy of Rice Seeds after Storage and Pre-Treatment with Dry Heat and Chemical Agents

Inappropriate seed packaging and seed dormancy affects seed quality and consequently leads to reduced crop stand, low seedling vigour and reduced yields. The objective of the study was to determine the effect of seed packaging material and seed treatment on viability and dormancy in rice seeds. Effect of packaging material was evaluated by storing freshly harvested seeds of Basmati 370 and BW 196 varieties in polythene, khaki, cheese cloth, polypropylene (Pp) sack and gunny bag sat room temperature and at 6 oC for six months. Effect of seed treatment on dormancy was determined by pre-treatment of seeds with nitric acid at 0.1 M, 0.2 M, 0.5 M, 1 M and 2 M, gibberellic acid (GA3) at 1000 ppm, 2000 ppm and 5000 ppm, and hydrogen peroxide at 0.5 M, 1 M, 2 M, 3 M, 5 M and dry heat at 50 oC for 48 hours. The seeds were subjected to germination test on moist paper and data on percentage germination, seedling length and seedling dry weight were taken. Packaging material had a significant (P ≤ 0.05) effect on germination and vigour. At room temperature, seed stored in polythene bag had the highest germination 88.2% and 57.8% for BW 196 and Basmati 370, respectively. Basmati 370 in khaki bag stored in the cold room had the highest germination 48.3%, while BW 196 stored in polythene had the highest (86.0%). Pre-treatment of seeds reduced dormancy, with variety BW 196 showing the highest germination of up to 67%, while variety Basmati 370 had the lowest germination of up to 40%. Gibberellic acid (GA3) at 5000 ppm was the most effective in breaking seed dormancy resulting in up to 95.7% germination. The results of the study indicated that packaging rice seed in polythene bags for periods not exceeding six months and pre-treatment with GA3 maintains high seed viability and breaks dormancy, respectively, thus ensuring rapid and uniform germination of vigorous seedlings. This would reduce the period farmers have to wait after harvest before they can plant newly harvested rice seeds.

English

The effect of Mucor racemosus and Rhizopus nigricans inoculation (g and 0.1 g L-1 distilled water) and a seed dressing fungicide Seedplus® (1.25 g 0.5 kg-1 seeds) on germination and seedling vigour of watermelon (cv. Chaliston gray) was investigated. The experiment involved a complete randomized design (CRD) with three replicates. It was confirmed that the combined inocula with higher density caused significantly poor germination and low seedling vigour (P ≤ 0.05) than those seeds inoculated with lower inocula density. Higher germination percentage and seedling vigour were observed with single fungus inoculation than with the two fungi inoculation. Dressing of the fungi-infected seeds with Seedplus® 30 WS significantly improved germination percentage and seedling vigour of watermelon (P ≤ 0.05) but not as high as that of the control. Key words: Mucor racemosus, Rhizopus nigricans, Seedplus.

Variability in the number of stems in Lotus tenuis seedlings growing at high density

Successful establishment of Lotus tenuis, an important legume to improve grasslands in the Pampa Deprimida, might be limited by low seedling vigor. The number of crown stems is an important component of vigor. The objective of this work was to determine the variability in the number of crown stems on seedlings of 11 Lotus tenuis natural populations sown at high density under semi-controlled conditions. Seeds of all populations were collected in the Province of Buenos Aires, Argentina. They were sown in plastic pots and cultivated in a greenhouse. Eight weeks after seeding, seedlings of each population were grouped according to their number of stems per crown. Variability in the crown stem number was studied within and among populations. Number of seedlings with different stem crown numbers within each population, dry weight (PS) of the group of individuals and mean for each group, the predominant groups of crown stem numbers from the total number of seedlings within each population, and those that presented a greater grouped dry weight and average per individual of each group were also determined. Simple linear regression of the crown stem numbers versus dry weight was conducted. ANOVA and Tukey´s tests were used (p≤0.01). The relationships between crown stem numbers and number of seedlings within each population tended to bimodal in 10 out of 11 populations. The crown stem number presented differences among (p≤0.01) and within (variation coefficient=44 to 56%) populations. Classes of 1 to 3 stems per crown were dominant (p≤0.01). Groups of 3 or 5 stems per crown showed greater dry weight (p≤0.01) when they were grouped or taken as a mean per individual, respectively. The regression was significant (p≤0.01) for mean dry weight per individual. Using of high density allowed the expression of variability within and among populations in the number of stems per crown. This variability can be attributed to genetic causes, considering the semi-controlled conditions under which the experiment was conducted. This implies the possibility of improving such parameter and the seedling vigor indirectly.

Expression of <I>GMCHI</I> Gene, Isolated from Soybean, Enhances the Survival in Prokaryotes to Low Temperature Stress

Low temperature during germination being a natural disaster usually occurs in North of China, which results in low germination rate and low seedling vigor, and even ultimately severe loss in yield. A gene was isolated from soybean Zhonghuang 22 cultivar (tolerant to low temperature in imbibition) for 24 h under 4℃ via cDNA-AFLP, name as GMCHI, GenBank accession No. EU699765. The full-length sequence of GMCHI which was 387 bp in nucleotide was obtained by RACE method. The se- quence of gene shared low similarity with that of genes documented in NCBI. Therefore we inferred that GMCHI was a new gene discovered in soybean. Semi quantitative RT-PCR result revealed that GMCHI was induced by ABA and IPEG.. The gene ligated with Prokaryotic expression vector was transformed into prokaryotic cell, the result of 6% SDS-PAGE induced by IPTG was ex- pressed in Prokaryotes. The E. coli carrying GMCHI survived and showed tolerance to low temperature under the treatment of ?20℃ for 2 h. RT-PCR validated that GMCHI in Prokaryotes improved the adaptation to low temperature.

Screening Citrus Rootstocks and Related Selections in Soil and Solution Culture for Tolerance to Low-iron Stress

A broad range of plant selections across the orange subfamily Aurantioideae were screened in solution and soil culture for their tolerance to low iron (Fe) stress. Young seedlings grown in soil were transferred to tubs of +Fe nutrient solution, which was later replaced after a brief period with a –Fe solution. Over several trials, ≈20 white root tips were harvested periodically from the plants in each tub and assayed for their ability to reduce Fe3+. The procedure was miniaturized to determine if a fewer number of root tips could be assayed to screen individual plants and to estimate the required sample size. For solution screening, seven root tips were estimated to be adequate for representing a single plant. Seedlings of a few selections were also grown in small containers of soil amended with 0% to 5.9% CaCO3. The results in solution and soil culture were consistent with each other and with previous assessments of the various selections. Based on a summary of the solution and soil responses, the citrus selections were grouped in descending order of Fe3+ reduction rates as Volkamer lemon/Rangpur/sour orange selections/Citrus macrophylla > mandarins and mandarin hybrids > citranges > citrumelos > trifoliate orange. Of the citrus relatives tested in solution culture only, those in the genera Glycosmis, Citropsis, Clausena, and Murraya had high Fe reduction rates with good seedling growth and new leaves developed a light yellow color or showed no loss of greenness. Other citrus relatives in the genera Severinia, Atalantia, and Fortunella and most somatic hybrids had low seedling vigor and produced too few root tips to be properly assessed. The results are useful because of the breadth of selections screened, the identification of various citrus relatives as potential sources of low-Fe stress tolerance in breeding new rootstocks, and the apparent positive relationship between the Fe3+ reduction responses, soil screening responses, and field experiences with carbonate-induced Fe chlorosis responses.

Competition, light quality and seedling growth of Russian wildrye grass (Psathyrostachys juncea)

The low seedling vigour of Russian wildrye grass ( Psathyrostachys juncea ) (RWR) limits its use. Shading from durum wheat ( Triticum turgidum ) reduced RWR leaf number, tiller number, leaf area and seedling dry weight in a growth room experiment. Treatments with similar shading differed in tiller number and dry weight, which suggested that light quality may have also contributed to these responses. In a second growth room experiment, light intensity (PAR) and red:far-red light ratio (670:730 nm) were altered by coloured plastic filters suspended above seedlings of Russian wildrye, crested wheatgrass ( Agropyron desertorum ) (CWG) and Dahurian wildrye grass ( Elymus dahuricus ) (DWR). Leaf area, tiller number and dry weight of RWR seedlings were reduced by declining red:far-red light ratio while light intensity differences at similar red:far-red ratio did not affect these variables. CWG exhibited similar responses to declining red:far-red light ratio as RWR, except that it exhibited a seedling weight response to light intensity. DWR tiller number was not responsive to low red:far-red light ratio but rather to low light intensity. However, DWR seedling weight, tiller weight and leaf area were responsive to declining red:far-red light ratio. These results indicate that RWR seedlings are sensitive to light quality changes caused by neighbouring plants.

Impact of Incorporation, Mulch, and Root Coating on the Establishment of Kura Clover from Rhizome Segments on Mine Spoils in Southeastern Kentucky

Kura clover (Trifolium ambiguum M. Bieb.) may have a place in surface mine reclamation, but low seedling vigor of currently available varieties limits establishment. The objectives of this study were to compare the effect of incorporation method, mulch, and a water-conserving mycorrhizal root coating (1998 only) on the establishment of kura clover from rhizome segments to a conventionally seeded control. Mulching increased plant density in sprigged treatments at the end of the establishment year (P< 0.05). Incorporation treatments that included disking increased plant density in Trial 1 but not in Trial 2. In Trial 2, the water-conserving mycorrhizal root coating negatively impacted sprig survival, resulting in lower plant densities one year after planting (P< 0.05). In fall of the establishment year, stand counts were higher for the conventionally seeded plots (P< 0.05). The following spring, seeded plots had more plants in Trial 1 (P< 0.05), but not in Trial 2. In Trial 2, competition from annual lespedeza [Kummerowia striata (Thunb.) Schindler] resulted in smaller seedlings at the end of the establishment year, and most likely contributed to the decreased ability of the conventionally seeded plants to over winter. Only the mulched-seeded treatment in Trial 1 had a satisfactory stand one year after planting.

Seedcoat Structure and Oxygen-enhanced Environments Affect Germination of Triploid Watermelon

Triploid or seedless watermelon [Citrullus lanatus (Thunb.) Matsum &amp; Nakai] cultivars often have erratic germination and low seedling vigor. The morphology of the seedcoat on two triploid cultivars—Tri X 313 and Tri X Sunrise—was examined by scanning electron microscopy (SEM) to identify structural differences compared to diploid seeds. Triploid seeds incubated with oxygen-enhanced treatments that included nicking, 1% hydrogen peroxide (H2O2), and 40% oxygen were investigated at low and high medium moisture levels. Triploid seed has a thicker seedcoat with a dense endotesta layer and a larger and highly variable air space surrounding the embryonic axis as compared with diploid seed. All cultivars rapidly imbibed water (≈50% of the original weight) during the first hour of imbibition, with a faster increase for triploids than for diploids. High moisture affected germination to a lesser extent in diploid than triploid seeds. Triploid germination under low medium moisture ranged from 96% to 76%, but was severely reduced to &lt;27% under high medium moisture. Triploid seed germination was significantly improved at high moisture by H2O2 and by 40% oxygen. Triploid watermelon seed is very sensitive to submerged conditions, possibly due to a combination of physiological and morphological defects. The rapid imbibition and excess water collected in the seedcoat and air space surrounding the embryo, could reduce oxygen diffusion and impair metabolic pathways leading to normal germination and seedling development.

Recurrent Selection for Seedling Vigor in Kura Clover

Kura clover (Trifolium ambiguum M. Bieb.) is a rhizomatous perennial forage legume that has outstanding persistence once established. Low seedling vigor presents a challenge to kura clover establishment. Kura clover seedlings partition a significant portion of their dry matter to below ground growth. Therefore, seedling vigor could be improved by increasing dry matter allocation to the shoot. Our objective was to study the potential of recurrent phenotypic selection in the greenhouse for reduced root/shoot ratio to increase seedling vigor. Three cycles of divergent selection for root/shoot ratio and a control selection for large plant biomass (LP) were performed from a parent population consisting of ‘Rhizo’, ARS‐2678, KZ1, and Erect Spreader populations. Selections for low root/shoot ratio (LoRS) and high root/shoot ratio (HiRS) were performed by independent culling after first selecting for large total biomass. Parent and selected populations were evaluated in the greenhouse and field. Three cycles of selection for LoRS and LP increased shoot yield in the field 42 d after planting (DAP) by 35 and 34%, respectively. Three cycles of selection for LoRS reduced root/shoot ratio in the field by 16%. Selection for HiRS did not affect seedling size in the field. Population mean shoot and total plant weights were correlated between greenhouse and field environments (average r = 0.89). Population mean seed weight was correlated with shoot weight in the field (r = 0.68, P &lt; 0.05). The results indicate that phenotypic greenhouse selection for seedling size is an effective means of increasing seedling vigor in kura clover.

Response of Incomplete Tifton 9 Bahiagrass Stands to Renovation

Establishment of warm-season grasses from seed is often impeded by slow germination and emergence, and low seedling vigor. Stand development can be further retarded by unfavorable soil moisture resulting from high temperatures and erratic precipitation. Management of poorly established stands of warmseason grasses has received limited research attention. Two- or 3year old, poorly established stands (basal occupation 0.05) than the control. Bahiagrass stands with at least a few plants per m 2 should be managed to minimize weed encroachment, but introducing additional seed, with or without tillage, offered no benefit.