Effect of irrigation applied at different growth stages and length of irrigation period on quality characters of potato tubers

Summary Potatoes were irrigated at three growth stages: (1) planting-stolon initiation. (2) stolon initiation-tuber bulking, and (3) tuber bulking, when available soil water dropped to 25%, 50% and 75%, bringing it up to field capacity; and irrigation ceased 0, 10 and 20 days before maturity. Significant increases in specific gravity, dry matter, starch content, chip yield and significant decreases in protein content and oil absorption rate of chips were observed due to the frequent irrigation at growth stages 1 and 2. No significant effect on chip colour was attributed to irrigation during the early growth stages. Frequent irrigations at the final growth stage were found to have deleterious effects on specific gravity, dry matter, starch content and chip yield especially when irrigation continued until maturity.     

Retardation of shoot growth and promotion of tuber growth of potato plants by paclobutrazol

The relationship between shoot growth and tuber yield in potato plants (Solanum tuberosum L. cv. Russet Burbank) was studied under greenhouse conditions using paclobutrazol [(2R,3R + 2S,3S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(l,2-4-triazol-l-yl)-pentan-3-ol), PP333], a growth retardant. Concurrent with reduction of stem elongation by the application of paclobutrazol to base of the main stem was a decrease in the dry weight of the shoot and an increase in the dry weight of the tuber. The inhibitory effect of paclobutrazol on stem elongation was reversed by gibberellic acid A₃ (GA₃). Leaf content of raffinose sugar and chlorophyll increased upon paclobutrazol treatment.     

Tolerance of selected weed species to broadcast flaming at different growth stages

Organic producers rank weeds as the most important pests that limit their crop production. In order to optimize the use of propane flaming as a weed control tool, the objective of this study was to test tolerance of selected weed species to broadcast flaming performed at different growth stages. Six annual species, including one grass [barnyardgrass (Echinochloa crus-galli)] and five broadleaves [field bindweed (Convolvulus arvensis), kochia (Kochia scoparia), ivyleaf morning glory (Ipomoea hederacea), velvetleaf (Abutilon theophrasti) and Venice mallow (Hibiscus trionum)] were flamed at three growth stages with six doses of propane. The propane doses applied were 0, 12, 31, 50, 68 and 87 kg/ha. Flaming treatments were applied utilizing a custom built flamer mounted on a four-wheeler moving at a constant speed of 6.4 km/h. Species response to propane were described by log-logistic models based on visual injury ratings and dry matter (DM) for each weed species. Overall response to flaming varied among species, growth stage and propane dose. Broadleaf weeds were more susceptible to flaming than the grass regardless of the growth stage. A dose of 76 kg/ha of propane was needed to obtain 90% DM reduction for 7-leaf (L) barnyardgrass compared to much lower doses of 40, 49, 55, 56 and 51 kg/ha propane for 8-L bindweed, 6-L kochia, 10-L morning glory, 7-L velvetleaf and 5-L Venice mallow, respectively. Moreover, the tolerance of both grassy and broadleaf weed species to broadcast flaming increased with increase in plant size. A 90% DM reduction in velvetleaf was obtained with 42, 56 and 102 kg/ha of propane for 5-L, 7-L and 16-L stages, respectively. The tested broadleaf weed species were effectively controlled (90% DM reduction) with propane dose of 30–60 kg/ha when flamed at early growth stages (3-L to 14-L), while the same dose of propane provided only 80% DM reduction in barnyardgrass when flamed at vegetative stages (4-L to 7-L). It was not possible to obtain 90% DM reduction in barnyardgrass when flamed at flowering stage with the propane doses tested in this experiment.     

Acquisition of potato leafroll virus byMyzus persicae from secondarily-infected potato plants of different genotypes

Summary The acquisition of potato leafroll virus (PLRV) byMyzus persicae nymphs from the top leaves of potato plants was studied throughout a growing season in relation to the antigen titre in those leaves and the feeding behaviour of the aphid. Secondarily-infected plants of eight potato genotypes with different levels of field resistance served as virus sources. Early in the growing season, plants were efficient sources for virus acquisition. The amount of viral antigen detected inM. persicae nymphs fed on the top leaves was strongly correlated with the titres of viral antigen in these leaves. Virus acquisition from the top leaves of older potato plants was markedly impaired and could not be correlated with their virus titre. With increasing age of the potato plants and the development of virus symptoms, the virus titre in the leaves declined and the initial weak correlation between the virus titre and field resistance ratings disappeared. Thus, screening secondarily-infected potato plants for field resistance to PLRV based on the concentration of viral antigen in leaves or in aphids fed on them should be avoided later in the growing season. The feeding rate ofM. persicae, measured by the number of honeydew droplets excreted, did not account for the reduced uptake of virus from older plants since it was not influenced by the age of the plant. Throughout the growing season, the feeding rate ofM. persicae nymphs on PLRV-infected plants was higher on genotypes with low levels of field resistance to PLRV than on genotypes with high ones.     

Respiratory oxidation by mitochondria from tomatoes at different stages of ripeness

A number of factors in the isolation of good quality mitochondria from tomato fruit wall tissue have been critically examined. Particles from tomatoes at a number of stages during maturation and senescence were isolated and their ability to oxidise succinate, malate and -ketoglutarate tested. In general, oxidation rates of the mitochondria and their respiratory control and ADP to oxygen uptake ratios reached a maximum with incipient ripeness and then declined with the onset of senescence. Thiamine pyrophosphate increased the oxidation rate of malate and -ketoglutarate at all stages and appeared to prevent instances of inhibition probably due to the accumulation of oxaloacetate. Particles from the green side of blotchy fruit had characteristics similar to those from normal fruit at the mature green stage, while the red side yielded particles that were similar to those from evenly coloured overripe fruit. Fruit having the dominant allele Never ripe, which causes extreme slowness in ripening, appeared to have mitochondria comparable in behaviour with those isolated from fruit undergoing normal maturation and senescense.

---

Zusammenfassung Eine Reihe von Faktoren, eine gute Qualität von Mitochondrien aus Fruchtschalengeweben von Tomaten zu isolieren, wurde kritisch untersucht. Teilchen von Tomaten einer Reihe von Reife- und Altersstadien wurden isoliert und ihre Fähigkeit geprüft, Succinat, Malat und -Ketoglutarat zu oxidieren.Im allgemeinen erreichen die Oxidationsraten der Mitochondrien und ihre Steuerung der Atmung sowie die ADP/O-Aufnahme-Verhältnisse ein Maximum mit beginnender Reife und nehmen ab mit einsetzendem Alter. Thiaminpyrophosphat erhöht die Oxidationsrate von Malat und -Ketoglutarat in allen Stadien und scheint Fälle von Hemmung zu verhindern, die wahrscheinlich auf eine Anhäufung von Oxalacetat zurückzuführen sind. Teilchen der grünen Seite fleckiger Früchte wiesen Charakteristika auf, die denen normaler Früchte im grünen Reifestadium entsprachen, während die rote Seite Teilchen ergab, die ähnlich denen normaler überreifer Früchte waren. Früchte mit dem dominanten Allel Never ripe, das ein extrem langsames Reifen hervorruft, scheinen Mitochondrien zu besitzen, die in ihren Eigenschaften denen vergleichbar sind, die aus Früchten normaler Reife und von normalen Alter isoliert wurden.

---

Resume Un certain nombre de facteurs intervenant dans l'isolement de mitochondries de bonne qualité à partir des tissus de la paroi du fruit de la tomate ont été examinés. Des particules extraites de tomates à différents stades de maturation et de sénescence ont été isolées et leur capacité d'oxyder le succinate, le malate et l'-cétoglutarate a été testée.En général, les vitesses d'oxydation des mitochondries, leur contrôle respiratoire et leur rapport ADP/O fixé atteignent une valeur maximum avec la maturité et puis décroissent avec l'instauration de la sénescence. L'addition de pyrophosphate de thiamine augmente la vitesse d'oxydation du malate et de l'-cétoglutarate à tous les stades et semble empêcher des inhibitions probablement dues à l'accumulation d'oxaloacétate. Des particules isolées de parties vertes de fruits blotchy présentent des caractéristiques similaires à celles extraites à partir de fruits normaux au stade de maturité verte, tandis que le côté rouge fournit des particules semblables à celles provenant des fruits trop mûrs uniformément colorés.Les fruits possédant l'allèle Never Ripe dominant, qui provoque une extrême lenteur dans la maturation, semblent présenter des mitochondries dont le comportement est comparable à celui des mitochondries isolées à partir de fruits subissant une maturation et une sénescence normales.

     

Tuberization in potato at high temperatures: response of physiologically young plants to disbudding and growth inhibitors

Summary In physiologically young plants (Solanum tuberosum L., cv. Sebago), abscisic acid (ABA) and chlorethyltrimethylammonium chloride (CCC) promoted tuberization at day/night temperatures of 32°/18°C, but not at 32°/28°C, in contrast to earlier experiments with physiologically old plants. Disbudding promoted tuberization at both temperatures. These results suggest that physiologically young plants have a greater capacity for increased gibberelling synthesis in the buds at high temperatures.     

The influence of stock and of scion on the growth and yield of potato plants produced by grafting cultivars of different maturity types

Summary The effect of stock and scion genotype on the growth and yield of potato plants was tested in large pots. In grafts between an early and a late-maturing cultivar the scion genotype had the dominant influence on most aspects of the growth. The stock had less influence, but stocks of cv. Pentland Dell (early main crop) supported less vigorous growth than those of cv. Cara (late main crop). Similar results were obtained in field plots lightly infested with potato cyst nematode. Ground cover measurements showed that compared with Cara, scions and stocks of Pentland Dell initially retarded growth to a similar degree but that later in the growing season the scion had a greater effect than the stock. The scion had a greater influence on the partitioning of assimilates and on haulm weight than the stock, but both the stock and the scion influenced final tuber yields.

---

Zusammenfassung Der Einfluss des Genotypes von Pfropfreis und Unterlage auf das Wachstum und den Ertrag von Kartoffelpflanzen, die durch Pfropfungen zwischen einer sp?t reifenden, einer frühen und einer frühen Hauptanbausorte (Tab. 1) hergestellt wurden, wurde in grossen T?pfen (30 cm Durchmesser) an Hand aufeinanderfolgender Ernten in w?chentlichen oder 2-w?chentlichen Abst?nden untersucht. Beim Mitteln der Ergebnisse aus den 9 aufeinander folgenden Ernten zeigte es sich (Tab. 2), dass das Wachstum der sp?t reifenden Sorte Cara durch die Pfropfung nur wenig vermindert wurde, und dass bei den Pfropfungen zwischen der Sorte Cara und der früh reifenden Sorte Pentland Javelin das Pfropfreis auf die meisten Wachstumserscheinungen den dominierenden Einfluss ausübte. In ?hnlicher Weise dominierte das Pfropfreis über der Unterlege bei Pfropfungen zwischen der Sorte Cara und der frühen Hauptanbausorte Pentland Dell, obgleich alle Knollen an der Unterlage erzeugt wurden (Tab. 3). Die Unterlagen von Pentland Dell tendierten jedoch, verglichen mit denen von Cara, zur Einschr?nkung des Spitzenwachstums. Dieser Unterschied im Einfluss wurde best?tigt, indem die ?nderungen der wichtigsten Leistungen des Pfropfreises (Abbildungen 2a–6a) und der Unterlage (Abbildungen 2b–6b) dargestellt wurden, wie das Trockengewicht der Spitze, das Trockengewicht der Wurzeln, das Trockengewicht der Knollen, das Gesamttrockengewicht und der Prozentsatz der gesamten Trockenmasse in den Knollen, Bei der Schlussernte, die 13 Wochen nach dem Umsetzen der Pflanzen in grosse T?pfe durchgeführt wurde, zeigte es sich, dass die Pfropfreiser von Pentland Javelin abgestorben (Tab. 4) und diejenigen von Pentland Dell teilweise senescent waren (Tab. 5). Insgesamt ergaben die Pflanzen von Cara auf Cara die gr?ssten Knollenertr?ge und die gr?sste Gesamttrockenmasse. Ein Versuch in Feldparzellen mit Pfropfungen zwischen den Sorten Cara und Pentland Dell ergab eine weitere Best?tigung der oben genannten Ergebnisse mit der Ausnahme, dass Messungen der Bodenbedeckung (Tab. 6) ergaben, dass die Unterlage anf?nglich fast ebenso viel Einfluss auf das Spitzenwachstum ausübt wie das Pfropfreis; Pfropfreiser oder Unterlagen von Pentland Dell verz?gern das Spitzenwachstum in gleicher Weise wie diejenigen von Cara. Der Einfluss des Pfropfreises vergr?sserte sich dejoch fortlaufend, so dass bei zwei Ernten, die nach 13 und 16 Wochen nach dem Auspflanzen ins Feld durchgeführt wurden, der Einfluss des Pfropfreises dominant über dem der Unterlage wurde (Tab. 7). Pflanzen von Cara auf Cara lieferten wieder die h?chste Gesamttrockenmasse und bei der Schlussernte waren die Pflanzen mit Cara Pfropfreisern noch grün und im Wachstum w?hrend diejenigen mit Pentland Dell Pfropfreisern senescent geworden waren.

---

Résumé L'influence du génotype du greffon et du porte-greffe sur la croissance et le rendement de pieds de pommes de terre produits par greffage entre variété tardive, précoce et demi-précoce est étudiée en grands pots (30 cm de diamètre) par arrachages échelonnés à une ou deux semaines d'intervalle. Les moyennes effectuées à partir des résultats des neuf arrachages montrent (tableau 2) que la croissance de la variété la plus tardive Cara n'est que légèrement ralentie par un greffage et que dans le cas de greffes entre Cara et la variété plus précoce Pentland Dell le greffon a l'influence la plus importante sur la plupart des différents aspects de la croissance. De fa?on semblable, dans le cas de greffes entre Cara et la variété précoce Pentland Dell le greffon domine sur le porte-greffe alors même que les tubercules sont formés sur le porte-greffe (tableau 3). Toutefois, les porte-greffes de Pentland Dell ont tendance à diminuer le développement de la partie aérienne par rapport à ceux de Cara. Cette différence est en effet confirmée si l'on figure graphiquement les principaux effets du greffon (figures 2a–6a) et du porte-greffe (figures 2b–6b) sur le poids sec de la partie aérienne, le poids sec des racines, le poids sec des tubercules, le poids sec total et le pourcentage de matière sèche totale dans les tubercules. Une récolte finale, effectuée 13 semaines après le transfert des plantes en grands pots, montre que les greffons de Pentland Javelin sont morts (tableau 4) et que ceux de Pentland Dell sont partiellement sénescents (tableau 5). Les pieds de Cara sur Cara produisent les meilleurs rendements en tubercules et en matière sèche totale. Une expérimentation en parcelles au champ, avec des greffes entre Cara et Pentland Dell confirme les conclusions précédentes à l'exception des mesures de couvertures du sol (tableau 6) qui montrent que le portegreffe a au moins autant d'effet que le greffon sur la croissance de la partie aérienne. Les greffons ou les porte-greffes de Pentland Dell retardent la croissance de la partie aérienne à un degré équivalent à ceux de Cara. Malgré tout, l'influence du greffon augmente progressivement, si bien que pour les deux récoltes effectuées 13 et 16 semaines après la plantation au champ, l'effet du greffon est plus important que celui du portegreffe (tableau 7). Encore une fois, les plantes de Cara sur Cara produisent la matière sèche totale la plus élevée et, à la récolte finale, les plantes avec greffon de Cara sont encore vertes et en croissance, tandis que celles avec greffon Pentland Dell deviennent sénescentes.

     

Effect of water stress at different development stages on vegetative and reproductive growth of corn

A field study was carried out from 1995 to 1997 in order to determine the effect of irrigation and water stress imposed at different development stages on vegetative growth, grain yield and other yield components of corn (Zea mays L.). The field trials were conducted on a silty loam Entisol soil, with Pioneer 3377 corn hybrid. A randomised complete block design with three replications was used. Four known growth stages of the plant were considered and a total of 16 (including rain fed) irrigation treatments were applied. The effect of irrigation or water stress at any stage of development on plant height, leaf area index, grain yield per hectare, as well number of ears per plant, grain yield per cob and 1000 kernels weight, were evaluated. Results of this 3-year study show that all vegetative and yield parameters were significantly affected by water shortage in the soil profile due to omitted irrigation during the sensitive tasselling and cob formation stages. Water stress occurring during vegetative and tasselling stages reduced plant height, as well as leaf area development. Short-duration water deficits during the rapid vegetative growth period caused 28–32% loss of final dry matter weight. Highest yields were observed in the fully irrigated control (VTCM) and the treatment which allowed water stress during the vegetative growth stage (TCM). Even a single irrigation omission during one of the sensitive growth stages, caused up to 40% grain yield losses during dry years such as 1996. Much greater losses of 66–93% could be expected as a result of prolonged water stress during tasselling and ear formation stages. Seasonal irrigation water amounts required for non-stressed production varied by year from 390 to 575 mm. Yield response factor (k_y) values (unitless parameter) relating yield loss to water deficits) obtained for the first, second and third experimental years were determined to be 1.22, 1.36 and 0.81, respectively.     

灵芝子实体不同生长阶段多糖与三萜类物质含量的研究

采用分光光度计法研究了灵芝芝蕾、芝柄、分化菌盖及成熟子实体等生长阶段的多糖与三萜类物质含量。结果表明,芝蕾发育阶段多糖含量最高,随着灵芝的生长发育,多糖含量逐渐降低;而三萜类物质含量则相反,芝蕾发育阶段最低,随着灵芝的生长发育逐渐升高,到成熟子实体阶段含量又略有降低。     

Evapotranspiration,yield, and water-use efficiency responses of Lesquerella fendleri at different growth stages

Lesquerella fendleri (Gray) Wats. is a potential new oilseed crop for the arid southwestern United States. Lesquerella seed oil with similar properties as castor oil is being considered as a domestic replacement for the imported castor oil. Development of new crops with low irrigation needs is of high priority. Because the most critical stage of sensitivity to moisture deficits has not been determined in Lesquerella species, the objectives of this study were: (i) to identify the most critical stage or stages for moisture deficit and, (ii) to determine the effect of moisture deficit on yield, yield components, oil and fatty acid composition. Two-year field studies were conducted at the New Mexico State University, Leyendecker Plant Science Research Center. The experimental design was a randomized complete block. The treatments consisted of (a) T1: Continuous favorable soil moisture [irrigated at 50% soil water depletion (SWD)]. (b) T2: Moisture stress (75% SWD) from establishment to initial flowering with no stress from flowering to final harvest (50% SWD). (c) T3: No stress imposed from establishment to initial flowering (50% SWD) followed by stress to final harvest (75% SWD). (d) T4: Moisture stress (75% SWD) from establishment to final harvest. The amount of water applied ranged from 810 to 729 mm for the first year, and 810 to 625 mm for the second year. Seed weight per plant and number of pods per plant were generally higher when water availability was maintained at or above 50% SWD throughout the growing season. Neither seed number per pod nor seed size was influenced by irrigation treatments. Lesquerella was more sensitive to water availability during flowering and seed development as a greater loss in seed yield occurred when irrigation was delayed to 75% SWD during that stage of development. Seed yield and dry matter production from the 2 year field studies were closely related to the seasonal cumulative evapotranspiration. For each millimeter of evapotranspiration, seed yield increased from 1.8 kg ha⁻¹ mm in 1994–1995 to 1.3 kg ha⁻¹ mm for 1995–1996. The dry matter production increased 13.4 kg ha⁻¹ for each mm increase in seasonal evapotranspiration during 1994–1995. This relationship was a second order polynomial with an R² of 0.86 during 1995–1996. The WUE_gr and WUE_dm were highest under the most favorable water availability conditions for growth and seed development. Delaying irrigation to 75% SWD throughout the crop growth period resulted in the lowest oil content. Lesquerolic acid content was not affected by irrigation during both the growing seasons.     

Elimination by chemotherapy of potato virus S from potato plants grown in vitro

Summary Potato virus S was eliminated from systemically infected stem cuttings of five potato cultivars after three passages in nutrient media containing 0.003% of the synthetic riboside ribavirin (Virazole). Treatment effects could be detected after only two passages which also revealed differences in cultivar response. Treated plants transferred to ribavirin-free culture media and to soil remained PVS-free. This simple method is less time-consuming than the usual meristem (axillary) tip culture procedures combined with chemotherapy or heat treatment.     

Growing potato plants by the water culture technique

A water culture technique was developed for the study of the nutrient requirements of the potato plant. Tuber formation was avoided by pinching off the stolons as they developed and hence vegetative growth could be studied without the complication of abnormal tuber formation in the culture solution. The K deficiency symptoms obtained by this method were essentially the same as those observed for field grown plants.     

Chemical composition of Flourensia cernua at four growth stages

Tarbush (Flourensia cernua DC) is an abundant Chihuahuan Desert shrub but is used sparingly by livestock. Leaves were removed from forty tarbush plants harvested in each of 3 years during four growth stages: (1) early. (2) mid-point, (3) late and (4) curtailed growth (ten plants per growth stage each year). Plants were air dried and all leaves were removed. In vitro dry-matter (DM) disappearance was greater for the early growth stage than other stages (P<005). The fibrous fraction increased with maturity, with neutral detergent fibre (NDF), acid detergent fibre (ADF) arid acid detergent lignin (ADL) contents all less for the early growth stage (P<0 05) than other stages. The latter three growth stages did not differ in NDF or ADF content, but ADL content was lower for the mid-point growth stage than for the two later stages (P<0–05). Calcium content increased with advancing season (P<0–05), whereas phosphorus concentration exhibited an inverse pattern (P<0–05). Nitrogen (N) content of tarbush was greatest in the early growth stage (P <0–05) and declined substantially thereafter. Soluble N content was greater and acid detergent insoluble N (ADIN) content was lower for early growth (P<005) than other stages. Insoluble N concentration followed a pattern similar to N, declining with advancing season (P<0–05). When expressed as a fraction of total N, insoluble N decreased and soluble N increased with maturity (P<005). Condensed tannin concentration tended (P<0–10) to increase with advancing season. Total phenolic content was lowest for early growth (P<005), and did not differ among the other stages. Chemical analysis revealed tarbush to be relatively high in N concentration. Fibre fractions, ADIN, ADL and condensed tannins were ail generally low whereas total phenolic content of tarbush was quite high. Early use by livestock would be most advantageous in terms of nutrient availability (N, P and in vitro digestibility) and lowest total phenolic concentration. Year-to-year variability in chemical composition of tarbush appears to be substantial. It remains to be seen whether overriding intake deterrents would be beneficial to livestock, given the high phenolic concentration in tarbush. Tarbush has several characteristics that make it a suitable model for studying plant-animal interactions of desert shrubs.     

The effect of moisture stress at three growth stages on the yield,components of yield and processing quality of eight potato varieties

A study was conducted over a three year period in southern Alberta to establish the yield and quality responses of eight potato varieties-Atlantic, Conestoga, Norchip, Niska, Shepody, Ranger Russet (Idaho clone), Ranger Russet (Amisk clone) and Russet Burbank to a single transient moisture stress (-80 kPa) at three growth stages in crop development (early, midseason and late). Early and midseason moisture stress had the greatest negative impact (P<0.05) on tuber yield. Of the eight varieties, Atlantic and Conestoga appear to be particularly sensitive to stress at these two growth stages. Midseason stress also appeared to reduce specific gravity. A year x stress interaction (P<0.05) for fry color suggests that the influence of moisture stress on fry color can be modified by other environmental factors. The results of the study demonstrate the importance of maintaining adequate soil moisture at all stages during crop development.     

Blackspot bruise susceptibility of potato tubers during growth and storage determined by two different test methods

Summary Blackspot bruise susceptibility of potato tubers of the cultivar Oleva increased during growth but was stable during storage independent of the type of impact method employed. With the pendulum test method, blackspots were observed in the tubers of the cultivar Dali during the final growth period and early in the storage period, whereas no blackspots were observed when they were treated on a shaking table. The relationships between blackspot susceptibility and dry matter content, size of starch granules, concentration of N, K, Mg and Ca, membrane leakiness and turgor pressure in the tuber cortices fluctuated according to cultivar, developmental stage of the tuber and the test method employed. The study underlines the importance of choosing a test method, which closely simulates the impact conditions of commercial situations, since the relationships between blackspot susceptibility and various physiological parameters of the tuber were found to change according to the impact condition employed.     

Plant water stress at various growth stages and growth and yield of soybeans

In the Southern High Plains of the U.S.A., where water for irrigation is being depleted, drought-tolerant crops are extensively grown under limited irrigation where less water is applied than is required for potential evapotranspiration and maximum yield. This study was conducted (1) to determine the effects of plant water stress at various growth stages on growth and yield of soybeans [Glycine max (L.) Merr.] and (2) to assess the adaptability of the soybean plant to limited irrigation in the stressful climate of the Southern High Plains. The 3-year study was conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). Soybeans (‘Douglas’, indeterminate, maturity group IV) were grown with different irrigation treatments designed to subject the plants to water deficits at different growth stages. Stress initiated during R1 (early flowering) or R2 (full bloom) and extending to R3 (beginning pod development) reduced seed yields by 9–13%. But, when stress was extended to R4.5, yields were reduced by 46%. Stress beginning at R3 and extending to R4.5 reduced yields by 19%. Stress imposed at R5 and relieved at R6 reduced yields 15% in one year and 46% in a more stressful year. Stress imposed at R5 and extending to the end of the growing period (5 weeks) reduced yields by 45% in the less-stressful year and by 88% in the other. Stress throughout the last 3 weeks of the growing period (beginning at R6) reduced yields by 21 and 65%, respectively, in the two years. Water-use efficiency was not increased under limited irrigation. Soybeans are amenable to limited irrigation under the stressful climate of the Southern High Plains, but their vulnerability to drought stress during seed development complicates management. They are more suited for limited irrigation than is corn (Zea mays L.) but are less suited than are grain sorghum [Sorghum bicolor (L.) Moench], cotton (Gossypium hirsutum L.) or wheat (Triticum aestivum L.).     

Carbon dioxide effects on potato growth under different photoperiods and irradiance

Carbon dioxide concentration can exert a strong influence on plant growth, but this influence can vary depending on irradiance. To study this, potato plants (Solanum tuberosum L.) cultivars Norland', Russet Burbank', and Denali' were grown in controlled-environment rooms at different levels of CO2 and irradiance. Carbon dioxide levels were maintained either at 350 or 1000 micromoles mol-1 and applied in combination with 12- or 24-h photoperiods at 400 or 800 micromoles m-2 s-1 photosynthetic photon flux. Air temperatures and relative humidity were held constant at 16 degrees C and 70%, respectively, and plants were harvested 90 d after planting. When averaged across all cultivars, CO2 enrichment increased tuber yield and total plant dry weight by 39 and 34%, respectively, under a 12-h photoperiod at 400 micromoles m-2 s-1; 27 and 19% under 12 h at 800 micromoles m-2 s-1; 9 and 9% under 24h at 400 micromoles m-2 s-1. It decreased dry weights by 9 and 9% under 24 h at 800 micromoles m-2 s-1. Tuber yield of Denali showed the greatest increase (21%) in response to increased CO2 across all irradiance treatments, while tuber yields of Russet Burbank and Norland were increased 18 and 9%, respectively. The results show a pattern of greater plant growth from CO2 enrichment under lower PPF and a short photoperiod.     

The response of potatoes to a single transient heat or drought stress imposed at different stages of tuber growth

Summary The effects of a single treatment of heat or drought stress imposed at different stages of tuber growth, were investigated in two potato cultivars, Désirée and Cara. Both stresses impaired dry matter accumulation in tubers, and tuber yields. Stress imposed at early stages of tuber growth, when tubers were less than 20 mm in diameter, had little effect on dry matter accumulation, whereas stress imposed later resulted ingnificant losses of dry matter in tubers. Stress imposed during later tuber growth increased the percentage of tubers sprouting in the soil. Tuber malformation was less affected. The adverse effects of heat on tuber yield and quality seemed to be greater than those of drought. Drought increased the content of total soluble solids (TSS) and lowered the osmotic potential in the tuber tissue of both cultivars. These effects were detectable even 55 days after stress relief. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel No 984-E, 1984 Series. This investigation was sponsored by a grant from the Ministry of Foreign Affairs, Technical Assistance Department, Netherlands.