Leaves provide substances and signals for pod and seed development in soybean. However, the regulatory feedbacks of pod and seed to leaf development remain unclear. We investigated the effects of pod and seed on leaf senescence by conducting pod removal and seed injury experiments. Pod removal and seed injury delayed leaf senescence and caused the staygreen phenotype of leaves. There were dosage effects of pod number on the extent of staygreen in depodded plants. The concentrations of chlorophyll (SPAD value, an index of relative chlorophyll content), soluble protein, and soluble sugar in the leaves of depodded plants were higher than those of intact plants. During seed development, the content of IAA decreased, while that of ABA increased. This trend was more pronounced in intact than in depodded and seed-injured plants. The GA₃/ABA ratio decreased gradually in all treatments. The content of GA₃ was relatively stable and was higher in intact than in depodded plants. The expression levels of four senescence-related genes, GmSARK, GmSGR1, GmCYN1, and GmNAC, declined in depodded or seed-injured treatments and were positively correlated with the number of leaves retained on plants. GmFT2a, the major flowering-promoting gene, was expressed at a higher level while E1, a key flowering inhibitory gene, was expressed at a lower level in depodded than in intact plants. We propose that the pod or seed can regulate leaf development. When the seed is aborted owing to disease infection or pest attack, the leaves stay green because of the absence of the seed signals for senescence.

Polyamines (PAs) are important endogenous plant growth regulators responding to environmental stress and mediating many physiological processes including grain filling in cereals. This study investigated whether PAs mediate the effect of post-anthesis soil drying on starch granule size distribution, starch content, and weight of superior and inferior kernels of wheat (Triticum aestivum L.). Two wheat cultivars were grown in pots. Three treatments, well-watered (WW), moderate soil drying (MD) and severe soil drying (SD), were imposed from 9 days post-anthesis until maturity. PA levels in kernels and small, medium and large granules were measured. The results showed that superior kernels had much higher free spermidine (Spd) and free spermine (Spm) concentrations, larger volumes of medium starch granules, and smaller-sized large granules than did inferior kernels under all the treatments. Compared to WW, MD significantly increased the concentrations of free Spd and free Spm, activities of soluble starch synthase and granule-bound starch synthase, volume of medium granules, and starch content and kernel weight of inferior kernels, and decreased the size of large granules. SD produced the opposite effect. Application of Spd or Spm to spikes produced effects similar to those of MD, and application of an inhibitor of Spd and Spm synthesis produced effects similar to those of SD. These results suggest that PAs mediate the effect of post-anthesis soil drying on starch biosynthesis in wheat kernels by regulating key enzymes in starch synthesis and that elevated PA levels under MD increase the volume of medium granules and kernel weight of inferior kernels.

The objective of this study was to identify the response of grain yield to plant density and nitrogen rate in spring maize hybrids released from 1970 to 2010 and grown extensively in Northeast China. Twenty-one hybrids were grown for 2 years in Northeast China at densities of 30,000, 52,500, 75,000, and 97,500 plants ha^{− 1} and N application levels of 0, 150, 300, and 450 kg N ha^{− 1}. Irrespective of density or nitrogen application rate, grain yields both per plant and per unit area were significantly higher for newer than older hybrids. As plant density increased from 30,000 to 97,500 plant ha^{− 1}, yield per plant of 1970s, 1980s, 1990s, and 2000s hybrids decreased by 50%, 45%, 46%, and 52%, respectively. The response of grain yield per unit area to plant density was curvilinear. The estimated optimum plant densities were about 58,000, 49,000, 65,000, and 65,000 plants ha^{− 1} for hybrids released in the 1970s, 1980s, 1990s, and 2000s, respectively. The theoretical optimum densities for the hybrids released from the 1970s to the 2000s increased by 1750 plants ha^{− 1} decade^{− 1}. Nitrogen fertilization significantly increased grain yields per plant and per unit area for all hybrids. The theoretical optimum N application rates for high yield for hybrids released in the 1970s and 1980s were about 280 and 360 kg ha^{− 1}, and the hybrids from the 1990s and 2000s showed highest yield at 330 kg ha^{− 1} N. No significant difference in the grain yields of 2000s hybrids between the N levels of 150 to 450 kg ha^{− 1} was found. Significant yield gains per plant and per unit area were found, with average increases of 17.9 g plant^{− 1} decade^{− 1} and 936 kg ha^{− 1} decade^{− 1} over the period 1970-2010, respectively. Yield gains were attributed mainly to increased yield per plant, contributed by increases in kernel number per ear and 1000-kernel weight. The rates of lodging and barren plants of newer hybrids were significantly lower than those of older ones, especially at high plant density.

Despite the great success achieved by the exploitation of heterosis in rice, the genetic basis of heterosis is still not well understood. We adopted an advanced-backcross breeding strategy to dissect the genetic basis of heterosis for yield and eight related traits. Four testcross (TC) populations with 228 testcross F₁ combinations were developed by crossing 57 introgression lines with four types of widely used male sterile lines using a North Carolina II mating design. Analysis of variance indicated that the effects of testcross F₁ combinations and their parents were significant or highly significant for most of the traits in both years, and all interaction effects with year were significant for most of the traits. Positive midparent heterosis (H_MP) was observed for most traits in the four TC populations in the two years. The relative H_MP levels for most traits varied from highly negative to highly positive. Sixty-two dominant-effect QTL were identified for H_MP of the nine traits in the four TC populations in the two years. Of these, 22 QTL were also identified for the performance of testcross F₁. Most dominant-effect QTL could individually explain more than 10% of the phenotypic variation. Four QTL clusters were observed including the region surrounding the RM9-RM297 region on chromosome 1, the RM110-RM279-RM8-RM5699-RM452 region on chromosome 2, the RM5463 locus on chromosome 6 and the RM1146-RM147 region on chromosome 10. The identified QTL for heterosis provide valuable information for dissecting the genetic basis of heterosis.

Increased productivity in sorghum has been achieved in the developed world using hybrids. Despite their yield advantage, introduced hybrids have not been adopted in Ethiopia due to the lack of adaptive traits, their short plant stature and small grain size. This study was conducted to investigate hybrid performance and the magnitude of heterosis of locally adapted genotypes in addition to introduced hybrids in three contrasting environments in Ethiopia. In total, 139 hybrids, derived from introduced seed parents crossed with locally adapted genotypes and introduced R lines, were evaluated. Overall, the hybrids matured earlier than the adapted parents, but had higher grain yield, plant height, grain number and grain weight in all environments. The lowland adapted hybrids displayed a mean better parent heterosis (BPH) of 19%, equating to 1160 kg ha^{− 1} and a 29% mean increase in grain yield, in addition to increased plant height and grain weight, in comparison to the hybrids derived from the introduced R lines. The mean BPH for grain yield for the highland adapted hybrids was 16% in the highland and 52% in the intermediate environment equating to 698 kg ha^{− 1} and 2031 kg ha^{− 1}_, respectively, in addition to increased grain weight. The magnitude of heterosis observed for each hybrid group was related to the genetic distance between the parental lines. The majority of hybrids also showed superiority over the standard check varieties. In general, hybrids from locally adapted genotypes were superior in grain yield, plant height and grain weight compared to the high parents and introduced hybrids indicating the potential for hybrids to increase productivity while addressing farmers' required traits.

Salt severely restricts cotton (Gossypium hirsutum) growth and production. The present study was undertaken to study the effect of salt-induced hydrogen peroxide (H₂O₂) on antioxidant enzymes in cotton. NaCl treatment or exogenous H₂O₂ was used to investigate the relationship between H₂O₂ content and levels of antioxidant enzymes including superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT), as well as the transcriptional levels of corresponding genes. H₂O₂ content increased within 24 h following 200 mmol L^-1 NaCl treatment. Both NaCl-induced and exogenous H₂O₂ increased the activity of antioxidant enzymes including APX and SOD and upregulated the transcriptional levels of GhcAPX1, GhFeSOD, and GhchlCSD. These increased activities and upregulated transcriptional levels were inhibited when the salt-induced H₂O₂ was scavenged by NAC. These results indicate that salt-induced H₂O₂ as a second signaling messenger modulates APX and SOD activities by regulating the transcription levels of corresponding genes, alleviating oxidative stress, and increasing salt tolerance in cotton.

Genotype and plant type affect photosynthetic production by changing the canopy structure in crops. To analyze the mechanism of action of heterosis and plant type on canopy structure in cotton (Gossypium hirsutum L.), we had selected two cotton hybrids (Shiza 2, Xinluzao 43) and two conventional varieties (Xinluzao 13, Xinluzao 33) with different plant types in this experiment. We studied canopy characteristics and their correlation with photosynthesis in populations of different genotypes and plant types during yield formation in Xinjiang, China. Canopy characteristics including leaf area index (LAI), mean foliage tilt angle (MTA), canopy openness (DIFN), and chlorophyll relative content (SPAD). The results showed that LAI and SPAD peak values were higher and their peak values arrived later, and the adjustment capacity of MTA during the flowering and boll-forming stages was stronger in Xinluzao 43, with the normal-leaf, pagoda plant type, than these values in other varieties. DIFN of Xinluzao 43 remained between 0.09 and 0.12 during the flowering and boll-forming stages, but was lower than that in the other varieties during the boll-opening stage. Thus, these characteristics of Xinluzao 43 were helpful for optimizing the light environment and maximizing light interception, thereby increasing photosynthetic capability. The photosynthetic rate and photosynthetic area were thus affected by cotton genotype as changes in the adjustment range of MTA, increases in peak values of LAI and SPAD, and extension of the functional stage of leaves. Available photosynthetic area and canopy light environment were affected by cotton plant type as changes in MTA and DIFN. Heterosis expression and plant type development were coordinated during different growth stages, the key to optimizing the canopy structure and further increasing yield.

NORK and soybean acyl carrier protein (ACP) both play important roles in nodulation. However, the relationship between Nod factor signaling and fatty acid (FA) biosynthesis during symbiotic development is unknown. In this study, an RNAi plasmid of GmNORK was constructed and transformed into soybean roots by Agrobacterium rhizogene-mediated hairy-root transformation. The nodule number decreased substantially in GmNORK knockdown soybean transgenic roots. To investigate the relationship between GmACP and Nod factor signaling, we measured GmACP expression levels in GmNORK RNAi soybean transgenic roots and found that rhizobia inoculation led to substantially reduced GmACP expression. Thus, FA biosynthesis was affected by Nod factor signaling during nodule development in soybean, a finding that provides valuable information that improves our understanding of the functions of GmNORK and GmACP in symbiotic signaling and nodule development.