Identification of QTL and candidate genes involved in early seedling growth in rice via high-density genetic mapping and RNA-seq

Early seedling vigor(ESV)is a major breeding target in rice,especially under direct seeding.To identify quantitative trait locus(QTL)affecting ESV,a recombinant inbred line population derived from a cross between 02428 and YZX,two cultivars differing in vigor during early seedling growth,was used for QTL analysis.Nine traits associated with ESV were examined using a high-density map.Of 16 additive loci identified,three were detected in two generations and thus considered stable.Four epistatic interactions were detected,one of which was repeated in two generations.Further analysis of the pyramiding effect of the three stable QTL showed that the phenotypic value could be effectively improved with an increasing number of QTL.These results were combined with results from our previous QTL analysis of the germination index.The lines G58 and G182 combined all the favourable alleles of all three stable QTL for ESV and three QTL for germination speed.These two lines showed rapid germination and strong ESV.A total of 37 candidate differentially expressed genes were obtained from the regions of the three stable QTL by analysis of the dynamic transcriptomic expression profile during the seedling growth period of the two parents.The QTL are targets for ESV breeding and the candidate genes await functional validation.This study provides a theoretical basis and a genetic resource for the breeding of directseeded rice.

Germination and early seedling growth of Pinus densata Mast.provenances

We studied seed germination and early seedling growth of Pinus densata to explore the range of variability within the species and to inform afforestation practices. Phenotypes were evaluated at a forest tree nursery under conditions that support Pinus yunnanensis, one of the presumed parental species of P. densata. Seeds were col- lected from 20 open-pollinated trees within each of eight autochthonous populations representing the natural distri- bution of P. densata in China to assess variation in ger- mination traits and early seedling growth, and to examine the relationships among these traits. Results showed that seeds from all populations germinated and seedlings established successfully. There were significant differences among populations in 13 of 14 traits evaluated. Seed germination and early seedling growth were strongly related to seed size and seed weight. Bigger seeds germi- nated earlier and faster than small seeds, and seedling size was positively correlated with seed size. Some germination traits were strongly and significantly correlated with cli- matic variables associated with the provenance of the studied populations. Based on these observations, we conclude there were large, significant, and biologically important differences among P. densata populations in seed germination and seedling growth traits. The observed variability probably reflects a high degree of adaptive dif- ferentiation among populations that is likely to be relevant for future afforestation.

Changes in Nutrient-Homeostasis and Reserves Metabolism During Rice Seed Priming:Consequences for Seedling Emergence and Growth

In this study influence of different seed priming treatments on the nutrient-homeostasis and reserve metabolism during seedling emergence and growth of rice were determined. Seed priming treatments included pre-germination, hydropriming for 48 h, osmohardening with KCl and CaCl2, ascorbate priming and hardening. All treatments shortened the emergence time and enhanced the energy and index of seedling emergence. Seedlings from primed seeds had greater length, number of roots and fresh and dry mass than control. Among the treatments, CaCl2, ascorbate and KCl proved better in enhancing emergence and seedling growth. Seed priming changed the pattern of N and Ca^2＋ homeostasis both of the seeds and seedlings, which were associated to enhancing s-amylase activity and reducing sugars content. Positive correlations of seedling attributes with nutrient content suggested that as a result of seed priming, most of N and Ca^2＋ were partitioned to embryo, which enhanced seedling emergence and subsequent growth of rice seedlings.

Improving Acacia auriculiformis seedlings using microbial inoculant(Beneficial Microorganisms)

A microbial inoculant, known as effective microorganisms （EM）, was applied to determine its efficacy on seed germination and seedling growth in the nursery of Acacia auriculiformis A Curm. ex Benth. The seedlings were grown in a mixture of sandy soil and cow dung （3：1） and kept in polybags; EM was poured at different concentra- tions （0.1%, 0.5%, 1%, 2%, 5% and 10%）. Seed germination rate and growth parameters of seedlings - shoot and root lengths, fresh and dry weights of shoots and roots, vigor, volume, and quality indices and stur- diness - were measured. The nodulation status influenced by EM was also observed, along with the measurement ofpigrnent contents in leaves. The highest germination rate （72%） was observed in 2% EM solution while the lowest （55%） was found in control treatment. The highest shoot and root lengths （30.6 cm and 31.2 cm respectively） were recorded in 2% EM and were significantly （p 〈0.05） different from control. Both fresh and dry weights of shoots were maximum （8.66 g and 2.99 g respectively） in 2% EM, whereas both fresh and dry weights of root were maximum （2.56 g and 1.23 g respectively） in 5% EM solution. Although the highest vigor index, volume index, and sturdiness （4450, 628 and 67.5 respec- tively） were found in 2% EM, the highest quality index （0.455） was found in 5% EM solution. The nodule number was higher at a very low （0.5%） concentration of EM but it normally decreased with the increase of concentration. The contents of chlorophyll a, chlorophyll b, and carotenoid were maximum （43.26 mg.L-1, 13.56 mg.L-1 and 17.99 mg.L-1 respectively） in 2% EM. Therefore, low concentration of EM （up to 2%）can be recommended for getting maximum seed germination and seed- ling development ofA. auriculiformis in the nursery.

Seed Size as Key Factor in Germination and Seedling Development of Copaifera langsdorffii(Fabaceae)

Seed size is a plastic trait of the plants that directly affect seed germination and seedling recruitment. This study aimed to investigate the relationship between seed size, seed germinability and seedling performance of Copaifera langsdorffii by testing four hypotheses: 1) larger seeds have higher germination percentage;2) smaller seeds require less time to germinate and for initial development of the seedlings;3) larger seeds produce more vigorous seedlings and 4) seed size negatively affects seedling root/shoot ratio. In 2011, we selected 30 individuals of C. langsdorffii from which 300 seeds were randomly collected in the plant canopy. All these seeds were weighted and placed in germination tray using vermiculite as substrate. Seed germinability and initial development of seedlings were monitored daily until cotyledons fell. Small seeds have higher germination percentage and germinate faster when compared to large seeds. Nonetheless, seedlings originated from larger seeds have longer development times, resulting in more vigorous seedlings. In addition, seedlings originating from small seeds allocate proportionally greater amount of resources to roots when compared to larger seeds. The fact that small seeds have higher germination percentage and faster germination favors the colonization of transient habitats. However, larger seeds produce more vigorous seedlings, favoring the seedling establishment in more stable habitats. Thus, we argue that high variability in seed size of C. langsdorffii favors its widespread geographic distribution.

Effect of Plant Derived Smoke on Germination and Post Germination Expression of Wheat (Triticum aestivum L.)

Smoke produced from burning of plant material elicits a striking increase in seed germination in various plant species. In present work, effect of plant derived smoke exposure on wheat (Triticum aestivum L.) seeds germination and post germination response has been studied in laboratory. Plant derived smoke was generated by burning of plant material (leaf, straws etc.) in a special designed furnace. Non-imbibed and imbibed seeds of wheat were exposed to plant derived smoke for 1 hr time duration. Best results were observed in non-imbibed seeds treated with plant derived smoke while imbibed seeds showed poor response to germination percentage, germination index, seedling vigor index and root shoot length. It has been proved from present study that plant derived smoke has stimulatory effect on germination & post germination response of non-imbibed seeds while it may cause inhibitory effect in imbibed seeds of wheat.

Plant growth-promoting characteristics of root fungal endophytes isolated from a traditional Cordillera rice landrace

This study was conducted to isolate and characterize the plant growth-promoting potential of fungal endophytes from the roots of Diket red,a traditional rice plant from the Cordillera,Northern Luzon.Eighteen morphospecies of filamentous endophytes were isolated of which twelve isolates were successfully identified to the species level.These isolates were identified as Aspergillus versicolor,Aspergillus sp.,Chaetosphaeria sp.,Cladosporium cladosporioides,Hypocrea lixii,Microascus murinus,and Trichoderma harzianum.The identified twelve isolates were selected to screen in vitro for their plant growth-promoting characteristics,and evaluated in vivo for their beneficial effects on seedling vigor and early seedling growth.Isolate PPL14 produced the highest IAA at 55.5μg ml^(-1)and M.murinus PPL10 produced the highest amount of IAA at 3.73μg IAA mg^(-1)dry mycelia wt.The seedling vigor assay and in vivo plant growth promotion bioassay indicated overall positive effects of culture filtrate(CF)application of the endophyte isolates.Rice seeds and seedlings grown in aseptic condition and treated with endophyte CFs displayed significantly enhanced levels of germination,seedling vigor,shoot,root,and total plant growth,and biomass compared to non-treated control.Other plant growth-promoting characteristics were also studied including phosphate solubilization,siderophore production,ammonia production,and catalase activity.This study supports the potential use of fungal endophytes as bio-inoculants for plant growth promotion and enhancement of nutrient assimilation of agriculturally important crops.

Thermal Hardening： A New Seed Vigor Enhancement Tool in Rice

Abstract: In a laboratory study, indica and japonica rice (Oryza sativa L.) seeds were exposed to thermal hardening (heating followed by chilling followed by heating; chilling followed by heating followed by chilling; heating followed by chilling or chilling followed by heating). In indica rice, heating followed by chilling followed by heating resulted in decreased mean germination time, time to start germination, electrical conductivity of seed leachates, and time to 50% germination, as well as increased germination index, energy of germination, radicle and plumule length, root length, root/shoot ratio, root fresh and dry weight, radicle and plumule growth rate, and shoot fresh weight. In japonica rice, chilling followed by heating followed by chilling performed better than all other treatments, including control.