Rate Of Dry Matter Accumulation Research Articles

Dynamics of Dry Matter Accumulation in the Developing Grains of Three Wheat Genotypes with Contrasting Grain Weight

AbstractThe accumulation of dry matter and its major components was studied in developing grains of two bold seeded (Selection‐111 and IWP‐5308) and one small seeded (kalyansona) wheat genotypes grown in pot culture condition. It was observed that in kalyansona, a sharp reduction in grain water content during the critical stage of grain enlargement limits its size resulting in compact filling of grains. In the developing grains of Selection‐111 and IWP‐5308, the high rate of dry matter accumulation was associated with their larger grain sink size. However, their lower grain density compared to kalyansona could be explained on the basis of non‐complementation between synthetic component and grain size (structural component). This non‐complementation may be due to relatively higher thermosensitive synthetic mechanism in the bold seeded genotypes.

Soil Fumigation, Fruit Production, and Dry Matter Partitioning of Field-grown Strawberry Plants

Bare-rooted `Camarosa' strawberry runner plants were established in a fruit production field on 1 Nov. 1993 using annual hill culture and two preplant soil fumigation treatments: 1) a mixture of 2 methyl bromide: 1 chloropicrin (wt: wt, 392 kg·ha-1) injected into the soil before forming raised planting beds (MBC); or 2) nonfumigation (NF). At about 33-day intervals between mid-January and the end of May, 20 plants were destructively sampled from each treatment to determine leaf dry mass (LDM), crown dry mass (CDM), root dry mass (RDM), and shoot: root dry mass (SRDM) ratios. Plant mortality was <0.2% throughout the study and did not differ with soil treatment. Regardless of sampling date, LDM, CDM, and RDM were greater for MBC plants than for NF plants, although treatment differences were not always significant. During the first 143 days, NF plants allocated a greater proportion of dry matter to roots than to shoots compared to MBC plants, indicating that roots are a stronger sink for photoassimilate in nonfumigated than in fumigated soils. However, there was no difference between treatments in SRDM by the end of the study. Fruit yield and a 10-fruit weight were determined at weekly intervals from mid-January until 23 May 1994. Yield and mean fruit weight of NF plants were 72% and 90%, respectively, of that of MBC plants. For both treatments, about one-half of total fruit production occurred between 144 and 174 days after planting (late March to late April). During that same period, rates of dry matter accumulation in leaf, crown, and root tissues decreased for plants in both treatments, but greatest reductions occurred in NF plants. Chemical name used: trichloronitromethane (chloropicrin).

Acúmulo de matéria seca e duração do período de enchimento de grãos do triticale

O experimento objetivou determinar a taxa de acúmulo de matéria seca e a duração do período de enchimento de grãos do triticale em Santa Maria - RS. Foram avaliadas cinco cultivares (BR I, BR 2, CEP 15, CEP 18 e IAPAR 23) no delineamento experimental em blocos ao acaso, nos anos de 1988 e 1989. A duração do período da antese à maturidade fisiológica foi de 45 dias, enquanto que o ciclo, da semeadura à maturidade fisiológica, foi de 156 dias, correspondendo a 676 e 1637 graus dias acumulados, respectivamente. A taxa de acúmulo de matéria seca nos grãos foi em média 0,694mg/dia e o peso médio de grão, estimado na maturidade fisiológica foi de 31,3mg. As cultivares estudadas de triticale apresentam diferentes taxas de acúmulo de matéria seca, o que permite o uso desta característica para a recomendação de cultivares em regiões que normalmente ocorrem altas temperaturas no final do período de enchimento de grãos. O peso médio de grão é associado à taxa de acúmulo de matéria seca e não ao período de enchimento de grãos.

Seasonal dynamics of mineral nutrients and carbohydrates by walnut tree leaves

Abstract The dry weight accumulation per leaf as well as the concentration per gram of dry weight and the accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined in walnut tree leaves (Juglans regia L.) during a complete life cycle. Additionally, the dynamics of plant nutrient concentration in leaf petiole sap and carbohydrate accumulation in leaves were studied in relation to the main life cycle events of the walnut tree. Total N, P, K, Cu, and Zn concentrations decreased, whereas that of Ca, Mg, and Mn increased during the season. Iron concentration fluctuated around a mean value. Total N, P, K, Mg, and Cu concentrations detected in younger mature leaves were at the sufficient level, whereas Ca, Fe, Mn, and Zn concentrations were at higher levels as compared to those previously reported. All the detected nutrient accumulations increased abruptly during leaf ontogeny and leaf maturation until a maximum level was attained in the younger mature leaves. Similarly, sucrose, glucose, and fructose accumulation were observed at the same period. The rates of total N, P, Cu, and Zn accumulation were lower than the rates of the observed dry matter accumulation and nutrient concentration dilution. Potassium and Mn accumulation rates were almost equal, whereas those for Ca and Mg were higher as compared to the dry matter accumulation rate. The fast embryo growing phase resulted in a considerable decrease in dry weight, total N, P, K, Cu, Zn, and carbohydrate accumulation, and to a lesser degree in Ca, Mg, and Mn accumulation. Nutrient accumulation reduction in leaves by the influence of the growing fruits were estimated to be: total N 52%, K 48%, P 29.5%, Mg 16.3%, Ca 15%, Fe 51.2%, Cu 55.2%, Zn 37.3%, and Mn 5.4% of the maximum nutrient value of the younger mature leaves. Old leaves preserved nutrients before leaf fall as follows: total N 25.4%, P 45%, K 31%, Ca 74.8%, Mg 76.5%, Mn 89.2%, Fe and Zn 50%, and Cu 37%. Nutrient remobilization from the senescing old leaves before leaf fall were: total N 22.6%, P 25.5%, K 21%, Ca 10.2%, Mg 7%, Fe 3.2%, Mn 5.4%, Cu 8%, and Zn 13.3% of the maximum value in the younger mature leaves. In early spring, the absorption rates of N, P, and Ca were low while those of Mg, Fe, Mn, Cu, and Zn were high. During the fast growing pollen phase, the N, P, Fe, Mn, Cu, and Zn concentrations were reduced. Calcium concentration is supposed to be more affected by the rate of transpiration rather than during the growing of embryo. Calcium and Mg concentrations in the sap were negatively correlated. The detected K concentration level in the sap was as high as 33 to 50 times that of soluble N, 12 to 21 times to that of P, 5 times to that of Ca, and 10 to 20 times to that of Mg. The first maximum of starch accumulation in mature leaves was observed during the slow growing embryo phase and a second one after fruit ripening. Old senescing leaves showed an extensive carbohydrate depletion before leaf fall.

Independence of nitrogen supply and seed growth in soybean: studies using anin vitroculture system

The effect of N supply on soybean (Glycine max L. Merrill) seed growth was investigated using an in vitro liquid culture system. Sucrose was maintained at 200 mM and N was supplied by asparagine and methionine in a 6.25 : 1 molar ratio. Media N concentrations from zero to 270 mM had little effect on cultured cotyledon dry matter accumulation rate for 7 or 14 d, but rates approached zero after 21 d when there was no N in the media. Only 17 mM N was required for maximum cotyledon growth rate up to 21 d. Cotyledon N accumulation and concentration increased in direct proportion to the N concentration in the media. The N concentration in cotyledons from a high protein genotype was higher than a normal genotype at all media N levels (0-270 mM). Soluble sugar and oil concentrations in the cotyledons were highest at zero media N and decreased as media N increased. These data suggest that the concept of seed N demand, which is thought to cause senescence in soybean, is incorrect. Soybean seeds can accumulate dry matter without accumulating N and apparently need only minimal supplies of N (17 mM) to maintain the metabolic enzymes necessary to sustain dry matter accumulation. Genetic differences in seed protein concentration seem to be regulated by the cotyledons not the supply of N.

Analysis of the Factors of High Yielding Ability for a Japonica Type Rice Line, 9004, Bred in China. II. The determining process of 1000 kernel weight.

Using the materials in the previous report, factors determining winnowed hulled 1000 kernel weight (WHTKW) of the primary (PRB) and secondary rachis branch (SRB) at different parts on an ear in line 9004 (L9), which is bred in China, as well as high yielding japonica type glutinous rice, were analyzed in comparison with a Japanese non-glutinous rice var. Koganemasari (KM). 1) For WHTKW of each part on an ear, it was generally shown that grains on both PRB and SRB of the top part in KM were heavier than those of the bottom part, however, the reverse pattern was shown in L9. Moreover, L9 had less difference in WHTKW between PRB and SRB than that of KM. Although WHTKW of each part on an ear was heavier in L9 than in KM, regardless of PRB and SRB, thc degree of difference on an ear between the two varied according to the part in the order bottom>middle>top parts and SRB greater than in PRB, in spite of little difference in hull weight. 2) Volume and specific weight of hulled grains of both PRB and SRB on each part on an ear were L9>KNI, KM>L9, respectively. Volume was significantly correlated with WHTKW in KM and L9, when compared separately or together. 3) The ripening period of grains on PRB or SRB of each part on an ear in L9 was the same or shorter than in KM, but L9 had a faster dry matter accumulation rate per grain than KM in the first half of ripening period (until 16 days after full heading time) due to the high moisture content in the ear. 4) The results mentioned above suggested that L9 had a faster dry matter accumulation rate for a grain viz. sink activity during thc first half of the ripening period due to a higher moisture content in thc ear compared with that of KM, resulting in superior WHTKW of L9 in both PRB and SRB of each part on an ear to KM.

Aerial dry matter and nutrient accumulation comparisons among five soybean experiments

Abstract Efficient and environmentally acceptable nutrient management requires an understanding of when and at what rates nutrients are accumulated by plants. For graminaceous species, a mathematical procedure involving compound cubic polynomials was previously demonstrated to be useful for evaluating growth and nutrient accumulation patterns. Our objective for this study was to compare dry matter and nutrient accumulation rates for determinate and indeterminate soybean [Glycine max L. (Merr.)] by reanalyzing the original data from five field experiments. Data from a maximum yield research (MYR) experiment that yielded 6.8 Mg ha‐1 provided information for soybean grown with near‐maximum accumulation rates. The high MYR yield resulted from intensive management practices that included high fertilization, high plant population, complete pest control, and timely irrigations to supplement rainfall. The MYR results were compared with rates determined for four non‐MYR studies that yielded from 2.2 to 5.4 Mg ha‐1...

Accumulation and Partitioning of Dry Matter in Taro [ Colocasia esculenta (L.) Schott

A field study was conducted as part of an ongoing effort to collect data on patterns of leaf area development and dry matter accumulation and partitioning among various plant parts during growth and development of two taro cultivars. Plants were harvested for biomass about every 6 weeks during the growing season. At each harvest, plants were separated into various plant parts, and their dry matter content was determined. The first 80 d after planting were characterized by low rates of dry matter accumulation, with only leaves, petioles, and roots showing substantial growth. Afterwards, increases in total dry matter were mainly the result of corm and sucker growth. Corm bulking occurred after the attainment of maximal leaf area indices. The absence of an optimal leaf area index for a longer period of time may have prevented the realization of higher dry matter yields. The partitioning of dry matter to the corms of both cultivars remained almost constant especially after 150 d after planting. This process was in contrast to the partitioning of dry matter to the suckers, which increased significantly until the end of the growing cycle.

Ear moisture during kernel development as influenced by field and laboratory selection

Grain quality, timeliness of harvest, and profitability can be increased by improving field drying characteristics of maize (Zea mays L.) hybrids. To better understand hows genes control ear drying, I compared maize strains developed by divergently selecting three cycles for (1) high HM or low LM moisture content at 45 d post pollination in the field or (2) fast FD vs. slow ear drying SD In laboratory. A field study across five locations compared HM, LM, FD, and SD strains from each of five synthetics for grain yield, ear moisture at harvest, test weight, lodging, and other agronomic traits. I studied ear moisture during grain filling for two subsets of divergently selected strains from one and three synthetics for 2 yr. In a third 2-yr field study, I measured mature kernel weight, lag period duration (LPD), effective grain-filling period (EFPD), and rate of dry matter accumulation (RDMA) for LM and HM strains developed from each of four synthetics. When averaged across the five synthetics, both SD and LM selections produced equivalent yields but lower ear moisture at harvest than the corresponding divergent strains. The LM strains had higher test weights than HM strains. When averaged across three synthetics and 2 yr, the HM strains produced higher moisture than LM strains at 15, 30, 45, and 60 d after silking. However, environments also influenced moisture content of the kernels during grain filling. In three of the four synthetics studied, HM strains had heavier kernels than corresponding LM strains. The heavier kernels seem to be due to increased RDMA. When averaged across four synthetics, LM strains had shorter LPD than HM strains. These correlated selection responses suggest that a genetic association exists among moisture content during grain filling, moisture content at physiological maturity, moisture content at harvest, LPD, and test weight. Breeding for LM or SD should improve field-drying characteristics of maize without increasing stalk breakage or decreasing yields. Key words:Zea mays L., grain filling, dry-down rates, mass selection, breeding methods

Physical Restriction of Pod Growth Alters Development of Soybean Plants

Efforts to determine the mechanistic relationships between fruit and canopy development are complicated by difficulties in designing nondestructive treatments that modify plant‐sink development. Pod growth was physically restricted by placing plastic straws, referred to as plastic pod‐restriction devices, over 0,50, or 100% of the soybean (Glycine max L. Merr.) pods in greenhouse experiments. The objective was to determine how decreases in pod growth influenced whole‐plant growth and development. Both the rate and final accumulation of seed dry matter were decreased by restricting pod growth. Conversely, restricting pod growth increased seed number due to increased production and decreased abscission of fruits. Plant dry matter and N accumulations during the linear seed‐fill period were not affected by restricting pod growth. This resulted from proportional increases in partitioning of assimilates into stems and leaves. Thus, decreases in reproductive growth apparently did not cause feedback inhibition of photosynthesis. Although leaf abscission was delayed by restricting pod growth, dry matter and N accumulation late in development were affected only slightly. In general, restricting pod growth influenced plant development and assimilate allocation in a similar manner as physical removal of fruits. The inverse relationship between the rate of dry matter accumulation in seed and pod and seed number per plant indicated that assimilate availability (united seed number. The delay in leaf yellowing and abscission induced by physically restricting pod growth suggested that the completion of monocarpic senescence was directly affected by changes in the rate of seed dry matter accumulation per plant.

Effects of Soybean Raceme-Order on Pod Set and Seed Growth in Three Cultivars.

The characteristics of pod set and seed growth as affected by raceme order were investigated to determine the yield-determining process of soybean. Observations of racemes were made on the 4th, 7th, 10th, 13th and terminal nodes of the main stem of three cultivars (Indeterminate type : Harosoy ; Determinate types : Enrei, Tamahomare). Pod-setting ratio and dry seed weight reduced in higher-order racemes, while the number of seeds in a pod did not vary among raceme orders. The lower seed weight of higher-order racemes was due to the short seed growth period. Compound leaves of secondary racemes enhanced the seed growth but not the pod-setting. With the highest node of determinate types, seed dry weight and rate of dry matter accumulation (RDA) of primary racemes exceeded those of terminal racemes, suggesting that more competition for assimilates among racemes occurred in terminal racemes. The results indicate that, regardless of growth habits, the lower the raceme order, the higher the number of pods and the pod-setting ratio. Seeds derived from lower-order racemes accounted for the majority of the yield. Hence, pod-setting and seed growth of lower-order racemes are more important than those of higher-order racemes in determining soybean yield.

Analysis of the Factors of High Yielding Ability for a Japonica Type Rice Line, 9004, Bred in China. 1. Comparison of yielding ability with a Japanese rice variety under the same level of spikelets number per area.

中国江蘇省で育成された多収性(日本型)水稲もち系統9004(L9)と対照品種として出穂期がほぼ等しいうるち品種コガネマサリ(KM)を供試し, 穂肥の窒素施用量の多少とリン酸施用の有無を組み合わせて栽培し, L9の多収要因の解析を行った. 両品種とも精玄米収量は, 主に1穂籾数の差に基づく面積当たり籾数の差によってL9では675～820gm-2, KMでは568～641gm-2で, 多窒素・リン酸施用区で最も高くなった. 収量はもみわら比と, またもみわら比はシンク容量(m2当たり籾数×精籾1粒重)と高い正の相関関係を示した. 穂肥のリン酸施用により, 1穂籾数の増大とそれに伴う登熟歩合の低下抑制により増収したが, その程度はKMよりL9で, また少窒素区より多窒素区で顕著であった. リン酸施用は, 窒素単独施用区よりもさらに葉色値を向上させ, 純同化率を高め, 登熟期間の乾物生産量を向上した. 一方, 両品種の各処埋区のm2当りの平均収量はL9では735g, KMでは588gで約150gの差がみられたが, これは主に千粒重の差異(L9:27.7g, KM:23.8g)によってもたらされた. 両品種の籾殻重と登熟期間には差異は認められなかったが, L9では登熟期間前半の籾の乾物蓄積速度がKMに比べて速く, このことが両品種の千粒重の差異の主要因と考えられた. これにはL9の籾の水分含有率が高く推移し, シンク活性が高かったこと, 穂揃期の稈+葉鞘の貯蔵炭水化物が多く, さらに稈から穂にかけての維管束系の発達がKMに比べて優っていたことが関係したと推定された.

TAXA E DURAÇÃO DE ACÚMULO DE MATÉRIA SECA E ÓLEO NOS GRÃOS EM DUAS CULTIVARES DE GIRASSOL

O objetivo deste experimento foi determinar a taxa e a duração do período de enchimento de grãos e acúmulo de óleo de duas cultivares de girassol (Contisol 711 e DK 180), sob duas densidades de plantas (50 e 70 mil pl/ha). Este trabalho foi realizado na Estação Experimental Agronômica/Universidade Federal do Rio Grande do Sul em Eldorado do Sul, RS, no ano agrícola de 1989/90. Para a realização das determinações foram coletadas, a partir da antese, oito plantas por subparcela, a cada sete dias. A densidade de plantas afetou o rendimento de grãos, de maneira variável conforme a cultivar, mas não influenciou a taxa e a duração de acúmulo de matéria seca nos grãos. A cultivar Contisol 711 apresentou período de enchimento de grãos 7 dias mais curto que a DK 180. De outra parte, a DK 180 apresentou maior taxa de enchimento de grãos. No presente trabalho não foi possível detectar se a taxa ou a duração do enchimento de grãos esteve mais associada com o rendimento de grãos e o teor de óleo nos grãos.

Development and Testing of Cultivar-Specific Tillering Coefficients for Sorghum

Tillering is an important yield component of grain sorghum [Sorghum bicolor (L.) Moench]. Temperature greatly influences tillering, and variability occurs among cultivars. Growth rate has been used to describe mathematically cultivar tillering abilities for a range of environments. Our objectives were to develop tillering coefficients for a range of temperate and tropical grain sorghum cultivars and to test the accuracy of these coefficients in predicting productive tiller numbers using independent field data. Eight grain sorghum cultivars of temperate (DK 39Y, DK 46, RS 610, and Pioneer 8500) and tropical adaptation (AT x 623 x RT x 430, DK E57, Segaolane, and CSM 63) were grown in a growth chamber at Manhattan under three day/night temperature regimes (20/150C, 25/200C, and 30/250C) to determine the relationship between dry matter required per tiller and daily minimum air temperature. Field experiments at St. John and Manhattan were used to determine the effects of dates and rates of planting on tillering of the same cultivars. The results were used to evaluate the accuracy of the tiller dry matter requirements. Growth chamber results showed that the number of tillers was related linearly to daily rates of dry matter accumulation per plant. These dry matter requirements per tiller were related linearly to daily minimum air temperature, with differences among cultivars. Predicted number of productive tillers per plant was approximately 7 to 12 times actual tiller numbers in the field experiments. This was accounted for by low cultivar-specific tillering coefficients, which were not representative of the dry matter requirement of productive tillers.

Growth Characteristics of Rhizoma Peanut and Nitrogen‐Fertilized Bahiagrass Swards

AbstractThe interaction of plant sensitivity to drought with N deficiency has been suggested as the reason grasses fail to persist under grazing when grown in association with rhizoma peanut (Arachis glabrata Benth.). To test this assumption, aboveground dry matter (DM) accumulation and relative growth rate (RGR) of ‘Florigraze‘ rhizoma peanut and ‘Pensacola’ bahiagrass (Paspalum notatum Flügge) fertilized with 0, 56, and 112 kg N ha−1 were measured from March to November in 1990 and 1991. Rhizoma peanut aboveground DM accumulation was greater both years (4950 and 6100 kg ha−1 1990 and 1991, respectively) in July at the start of the summer rainy season than any N‐fertilized bahiagrass treatment (640 and 1530, 1240 and 2330, and 1570 and 4490 kg ha−1 in 1990 and 1991 for 0‐N, 56‐N, and 112‐N treatments, respectively), due to higher RGR. Although the RGR of rhizoma peanut was similar to or less than that of the bahiagrass treatments for the remainder of the growing season in both years, by August 1991 only the 112‐N bahiagrass treatment (5260 kg ha−1) had total DM accumulation similar to rhizoma peanut (5110 kg ha−1). Rhizoma peanut RGR appeared to be more sensitive to rainfall, and was positively correlated (r = 0.71) with rainfall for as long as 8 wk prior to the sample dates in the dry spring of 1990. Bahiagrass RGR showed no correlation with rainfall either year. This suggests that lack of persistence of bahiagrass in mixed swards is due to severe competition for light with rhizoma peanut in springs when moisture is adequate and to potentially increased stress due to grazing in springs when drought restricts growth of rhizoma peanut.

Grain filling of R-nj color-selected maize strains divergently selected for kernel weight

Grain-fill characteristics in maize (Zea mays L.) affect yield by changing kernel weight. The objective of this study was to learn how divergent tandem selection for R-nj color expression and kernel weight affected rate of dry matter accumulation (RDMA), effective grain-filling period (EFPD), and lag phase duration (LAGP). We studied development of apical, mid-ear, and basal kernels in two genetic backgrounds. We derived 12 maize strains by tandem selection within each of two early-maturing synthetics. Mass selection of synthetics NDSF and NDSD for four cycles for high (HC), random (RC), and low (LC) R-nj color expression produced six substrains. Then, four cycles of divergent mass selection for kernel weight within each color-derived substrain produced 12 substrains for study. Using the 12 strains, we conducted field experiments using a completely random experimental design within each of 2 yr at Fargo, ND. Sequential kernel samples of individual ears within each strain provided data to estimate RDMA, EFPD, LAGP, and five-kernel weight (KWT). We sampled at 3- to 4-d intervals during the linear phase of grain-filling and at maturity. Selection for HC increased RDMA but tended to decrease EFPD compared to LC strains in both NDSF and NDSD. Selecting heavier kernels increased KWT of basal and mid-ear kernels by increasing RDMA. Direct and correlated responses to R-nj color selection were evident after four subsequent cycles of divergent tandem selection for kernel weight. Therefore, R-nj expression was not a temporary maternal effect. Kernel weight selection responses differed among the color strains and synthetics. Kernel weight seemed mainly determined by RDMA that was affected by selection for R-nj color expression and for kernel mass. Key words:Zea mays L., aleurone color, mass selection, correlation, yield components

Influence of N supply on development and dry matter accumulation of an old and a new maize hybrid

The response of an old and a new maize (Zea mays L.) hybrid to N supply was evaluated under controlled-environment conditions. An old hybrid (Pride 5) and a new hybrid (Pioneer 3902) were grown at three N levels (15, 2.5, and 0.5 mM N), and development and dry matter accumulation were measured at the 4-, 8-, and 12-leaf stage. Leaf chlorophyll was monitored from the 8- to 12-leaf stage, and leaf photosynthesis, stomatal conductance, and leaf chlorophyll fluorescence were measured at the 12-leaf stage. Rate of dry matter accumulation decreased with declining N supply. In contrast, decreasing N supply progressively increased the duration of the 4- to 8-leaf phase and the 8- to 12-leaf phase. As a consequence, total dry matter at the 12-leaf stage did not differ among N levels. The rate of leaf appearance of the old hybrid (Pride 5) was proportionately more reduced under low N than that of the new hybrid (Pioneer 3902). Similarly, the reduction in crop growth rate during the 8- to 12-leaf stage at the lowest N level was 46% for Pride 5 and 24% for Pioneer 3902. Leaf chlorophyll content was higher for Pride 5 than for Pioneer 3902 at high N levels, but leaf chlorophyll content declined significantly more rapidly in Pride 5 than in Pioneer 3902 when N stress increased. Leaf carbon assimilation rates were 4–27% higher for the new hybrid, with the largest differences occurring at low N levels. Collectively, results of this study show that the old hybrid (Pride 5) was more sensitive to N stress during early development than the new hybrid (Pioneer 3902). Key words:Zea mays L., nitrogen stress tolerance, chlorophyll content, photosynthesis, chlorophyll fluorescence

Partitioning of Dry Matter in Tanier (Xanthosoma spp.) Irrigated with Fractions of Evapotranspiration

The accumulation and partitioning of dry matter was determined in tanier plants irrigated with fractions of the water lost through evapotranspiration (WLET) in an effort to establish growth analysis data from which a tanier growth (simulation model could be developed. The irrigation regimes were based on Class A pan factors ranging from 0·33 to 1·32 with increments of 0·33. Tanier plants were planted in the field and harvested for biomass production about every 6 weeks during the growing season. At each harvest, plants were separated into various plant parts, and their dry matter content was determined. The first 90 d after planting (DAP) were characterized by low rates of dry matter accumulation, with only leaves and petioles showing substantial growth. A grand growth period followed in which leaves, petioles, and roots rapidly accumulated dry matter until 278 DAP. During this period, plants that received 0·99 and 1·32 WLET exhibited similar total dry matter content, and this was significantly greater than in plants supplied with 0·33 and 0·66 WLET. Cormel dry matter content peaked at 29% of total plant dry matter by 322 DAP in plants replenished with 1·32 WLET. Partitioning of dry matter to cormels in other treatments was significantly reduced. Partitioning of dry matter to corms increased linearly throughout the growing season in all treatments. Dry matter partitioning to suckers and the number of suckers formed from plants replenished with 0·33 and 0·66 WLET was greater than in the more irrigated treatments.

Control for Rate of Seed Development and Seed Yield Potential in Soybean

Selecting for increased weight per seed among male‐sterile soybean plants [Glycine max (L.) Merr.] increased seed weight and seed yield for male‐fertile progeny but had minimal effects on seed number per ha. Assimilate availability to the seed during selection was essentially nonlimiting for an extended period, since male‐sterile plants have few seeds per plant. For the observed range, seed weight has shown no association with seed yield potential. This study tested two alternate hypotheses to explain the increased seed yield potential: (i) selection identified genotypes with increased seed sink activity per plant or (ii) selection identified genotypes with reduced seed maturation rates. Dry matter accumulation rate (DMAR) per unit seed dry weight, DMAR per unit seed coat area, and rate of increase in seed density were determined for greenhouse‐grown plants using a 7‐d period during mid‐seed development. The following observations led to the acceptance of the reduced seed maturation rate hypothesis: (i) When assimilates were made essentially nonlimiting to the seed by partial pod removal, selected and nonselected populations had similar DMAR per unit seed coat area and per unit seed dry weight, (ii) Selection for seed weight on male‐sterile plants reduced the rate of increase in seed density. (iii) DMAR per unit seed coat area did not increase with selection. Selected and nonselected populations, had similar DMAR per unit seed dry weight. Apparently, selection had occurred against the reduction in rate of dry matter uptake by the seed. This reduction is normally associated with reduced seed maturation rate. Selection for seed weight on male‐sterile plants can be completed during the early generations of a breeding program and used to identify genotypes that have longer seed‐filling durations and more efficient systems for assimilate utilization.

The field pea crop in S.W. Australia. I. Patterns of growth, biomass production and photosynthetic performance in genotypes of contrasting morphology

Biological yield and photosynthetic performance of six field pea genotypes of contrasting foliar morphology and growth habit were studied in a water-limited field environment at Wongan Hills, Western Australia. Dundale and Wirrega were tall, indeterminate, scrambling and conventionally leaved; Dinkum, L82 and L80 (semi-leafless) and Progreta (tare-leaved) were semi-dwarf and more erect. Green area index (green leaf area per unit of ground area), green area duration (time integral of green area), crop growth rate (rate of dry matter accumulation per unit ground area) during early spring, net photosynthetic rate (CO2 exchange rate per unit green area or unit green weight) and net assimilation rate (rate of dry matter accumulation per unit green area) all influenced crop productivity. Shoot and root biomass was highest in Wirrega, due mainly to superior green area index, extended green area duration and maintenance of high growth rate during pod fill. Inverse relationships amongst genotypes were evident between green area index and net assimilation rate, and between green area index and CO2 exchange rate of green area. Total net photosynthesis of the tendrils of semi-leafless types was similar to that of leaflets of conventional types, due mainly to larger biomass of tendrils compensating for poor photosynthetic rates. The poor growth of semi-leafless and tare-leaved types was attributed to lower vigour, green area, ground cover and photosynthate production. Future selection of such types for water-limited environments should concentrate on increasing shoot height, node number per plant, stipule and tendril size and photosynthetic efficiency of green area.