Pathogenic aspects of Pantoea agglomerans in relation to cotton boll age and Dysdercus cingulatus (Fabricius) transmitting seed and boll rot in cotton germplasm

Bacterial seed and boll rot is a newly emerging cotton disease in Pakistan. Twenty-one cotton varieties were screened to find resistance source against the disease. None of these was found to be resistant. Five cotton varieties (CIM-595, MK2, BT-986, BT-986 & SG-1) having 700–1400 Area under disease progress curve (AUDPC) units were found to be moderately resistant to the disease. SLH-317, FH-942, BT-222, BT-666, MNH-457 ranging from 1401–1700 AUDPC units were moderately susceptible while MNH-456, SLH-336, 9811, FH-942, MNH-886 susceptible to boll rot. Seven varieties (FH-114, FH-113, BT-7, BT-212, SLH-BT-4, BT-212 and FH-941) were highly susceptible to bacterial seed and boll rot indicated by 2001–2300 AUDPC units. Biochemical tests identified bacterial isolates as Pantoea agglomerans. Different inoculation techniques were assessed for bacterial pathogenicity and symptoms of boll rot were only observed in needle punctured bolls. One, two and three weeks old bolls were mechanically inoculated by injecting bacterial suspension to evaluate the boll’s age impact on disease severity. Maximum severity was observed in two weeks old bolls. Red cotton bugs (Dysdercus cingulatus) were fed on artificially inoculated diseased bolls and then transferred on healthy bolls. Diseased symptoms were noticed on healthy cotton bolls. Bacterial colonies were recovered and red cotton bug was confirmed as the disease-transmitting vector.     

Oviposition on and mining in bolls of Bt and non-Bt cotton by resistant and susceptible pink bollworm (Lepidoptera: Gelechiidae)

Transgenic cotton that produces insecticidal crystal protein Cry1Ac of Bacillus thuringiensis (Bt) has been effective in controlling pink bollworm, Pectinophora gossypiella (Saunders). We compared responses to bolls of Bt cotton and non-Bt cotton by adult females and neonates from susceptible and Cry1Ac-resistant strains of pink bollworm. In choice tests on caged cotton plants in the greenhouse, neither susceptible nor resistant females laid fewer eggs on Bt cotton bolls than on non-Bt cotton bolls, indicating that the Bt toxin did not deter oviposition. Multiple regression revealed that the number of eggs laid per boll was negatively associated with boll age and positively associated with boll diameter. Females also laid more eggs per boll on plants with more bolls. The distribution of eggs among bolls of Bt cotton and non-Bt cotton was clumped, indicating that boll quality rather than avoidance of previously laid eggs was a primary factor in oviposition preference. Parallel to the results from oviposition experiments, in laboratory no-choice tests with 10 neonates per boll, the number of entrance holes per boll did not differ between Bt cotton and non-Bt cotton for susceptible and resistant neonates. Also, like females, neonates preferred younger bolls and larger bolls. Thus, acceptance of bolls by females for oviposition and by neonates for mining was affected by boll age and diameter, but not by Bt toxin in bolls. The lack of discrimination between Bt and non-Bt cotton bolls by pink bollworm from susceptible and resistant strains indicates that oviposition and mining initiation are independent of susceptibility to Cry1Ac.     

Single leaves photosynthetic characteristics of two insect-resistant transgenic cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.) varieties in response to light

How the photosynthetic characteristics of insect-resistant transgenic cotton (Gossypium hirsutum L.) respond to light or whether this genetic transformation could result in unintended effects on their photosynthetic and physiological processes is not well known. Two experiments were conducted to investigate the shapes of net photosynthetic rate (P _N), stomatal conductance (g _s), apparent light use efficiency (LUE_app) and water use efficiency (WUE) light-response curves for single leaves of Bt (Bacillus thuringiensis) and Bt+CpTI (cowpea trypsin inhibitor) transgenic cotton plants and their non-transgenic counterparts, respectively. Results showed that the significant difference in response of P _N and WUE to light between transgenic cotton and non-transgenic cotton occured but not always throughout the growing season or in different experiments or for all transgenic cotton lines. It was highly dependent on growth stage, culture condition and variety, but no obvious difference between any transgenic cotton and non-transgenic cotton in the shapes of g _s and LUE_app light-response curves was observed in two experiments at different growth stages. In the field experiments, transgenic Bt+CpTI cotton was less sensitive to response of P _N to high irradiance at the boll-opening stage. In pot experiments, WUE light-response curves of both Bt transgenic cotton and Bt+CpTI transgenic cotton progressively decreased whereas non-transgenic cotton slowly reached a maximum at high irradiance at boll-opening stage. We supposed that culture environment could affect the photosynthesis of transgenic cotton both directly and indirectly through influencing either foreign genes expression or growth and physiological processes.     

Removal of early fruit branches triggered regulations in senescence,boll attributes and yield of Bt cotton genotypes

Premature senescence, unopened and rotted bolls are the primary constrictions hampering the accomplishment of yield potential in Bt cotton. An experiment was conducted with the objectives to delay senescence, enhance boll opening and reduce the boll rotting. The experiment was conducted at two randomly selected sites of University of Agriculture Faisalabad, Pakistan, during 2015 and repeated in 2016. Each experiment was laid out in randomised complete block design with two by two factorial arrangement structure and replicated five times. Treatments were comprised of R₀ = no fruit removal; R₁ = removal of early fruit branches (REFB) and two genotypes, viz. V₁ = FH‐142 and V₂ = MNH‐886. Genotypes were selected on the basis of abiotic stress tolerance (FH‐142) and susceptibility (MNH‐886). Nodes above cracked bolls, monopodial branches, opened bolls per plant and seed cotton yield were enhanced by 23, 12, 13 and 17%, respectively, under the influence of REFB over no fruit branch removal, while the REFB‐mediated decrease in boll rotting was 27%. Moreover, the response of MNH‐886 was more remarkable than FH‐142 for all studied variables. Conclusively, REFB increased the number of nodes above a cracked boll, monopodial branches, opened bolls per plant and seed cotton yield while decreased rotted bolls per plant in both genotypes.     

Effect of water-deficit stress on cotton plants expressing the Bacillus thuringiensis toxin

Bacillus thuringiensis (Bt) crops require a high dosage of Bt toxin to delay development of insect resistance, in particular, when the refuge strategy is applied. This strategy is threatened by plant developmental and environmental factors that might reduce Bt toxin concentration and Bt efficacy in Bt crops. Growth of Bt (Cry1Ac) cotton under prolonged, moderate water deficit as a single stress factor was evaluated. Bt cotton plants were analysed for physiological performance, Bt toxin concentration and Bt efficacy. For performance analysis, leaf and total plant dry weight and leaf area were measured. Bt toxin concentration was determined by an immuno‐assay. Effects of Bt toxin on growth and mortality of African cotton bollworm, Helicoverpa armigera, larvae were measured in different plant organs. Leaves from young plants exposed for 30 days to moderate water deficit had both higher Bt toxin concentrations and were more effective against larvae than leaves, flowers or bolls from mature flowering plants exposed to 60 days of moderate water deficit. Although growth of Bt cotton plants under moderate water‐deficit conditions decreased Bt concentrations in leaves, flowers and bolls, this had no effect on efficacy against first‐instar cotton bollworm larvae. No significant evidence was found that moderate water deficit, as a single stress factor, decreases Bt efficacy in Bt cotton.     

Impact of transgenic cotton varieties on activity of enzymes in their rhizosphere

The impact of five Bacillus thuringiensis (Bt) cotton varieties and their respective isogenic non-Bt(NBt) isolines (ANKUR-2534, MECH-6304, RCH-317, ANKUR-651 and MECH-6301) was assessed on the key soil enzymes i.e., dehydrogenase, alkaline phosphatase and urease in their rhizosphere at four growth stages of the crop, namely vegetative, flowering, bolling and harvesting. These varieties were grown on farmer's field in villages 22 miles and 24 miles of Ganganagar District of Rajasthan State in India. Results showed that dehydrogenase, alkaline phosphatase and urease activities were higher in rhizosphere of Bt isolines as compared to NBt isolines of all the varieties. Except phosphatase, differences in dehydrogenase and urease activities in rhizosphere of Bt and NBt isolines of all five varieties were significant (P < 0.05). Maximum enhancement in the three enzymes activities was observed in MECH-6304 Bt isoline rhizosphere. Maximum and minimum activities of dehydrogenase and urease were observed in MECH-6304 and RCH-317 Bt isolines, respectively, whereas phosphatase activity was maximum and minimum in MECH-6304 and ANKUR-651 Bt isolines, respectively. Maximum dehydrogenase and urease activities were observed at boll formation and minimum at flowering and harvesting stage, respectively, while maximum phosphatase activity was observed at vegetative stage and minimum at harvesting stage. In conclusion, all the studied Bt isolines of cotton varieties showed no adverse effect on dehydrogenase, alkaline phosphatase and urease activities in the rhizosphere.     

转大肠杆菌过氧化氢酶基因棉花的抗旱生理研究

以导入大肠杆菌过氧化氢酶基因KatE的T3代转基因棉花为供试材料,经卡那霉素检测和PCR鉴定,将筛选出的阳性转基因植株与对照棉花进行整个生育期的持续水分胁迫处理直至收获,比较材料间的生理生化指标的差异,鉴定转基因植株的耐旱能力。结果显示:(1)干旱胁迫持续至初蕾期时,转基因棉花与对照植株间各项抗旱生理指标差异均未达到显著水平。(2)水分胁迫持续至盛蕾和盛花期时,转基因棉花叶片相对含水量、光系统Ⅱ最大光化学效率(Fv/Fm)、CAT活性,以及叶片的净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)均显著或极显著高于对照植株,叶绿素含量也都明显高于对照植株。干旱胁迫持续至吐絮期时,转基因棉花的株高、果枝数和铃数均显著或极显著高于对照植株,且转基因棉花和对照的籽棉产量分别比正常灌溉处理降低57.5%和60.1%,全生育期的水分胁迫严重影响了棉花籽棉产量,但转基因棉花的籽棉产量仍显著高于对照。研究表明,在新疆石河子当地自然降水(干旱胁迫)条件下,转KatE基因棉花表现出了较好的生理和生长优势,KatE基因有助于提高棉花的抗旱性。     

Genotypic variation for drought tolerance in cotton (Gossypium hirsutum L.): Leaf gas exchange and productivity

Although water-limited environments are detrimental to cotton growth and productivity worldwide, identification of cotton (Gossypium hirsutum L.) genotypes that are less sensitive to drought may improve productivity in drought prone areas. The objective of the study was to assess genotypic variation for drought tolerance in cotton varieties using physiological attributes as selection criteria, and to determine the relationship of physiological attributes with productivity traits. The association of target physiological traits for drought tolerance (photosynthetic rate (P_n), stomatal conductance (g_s), and transpiration rate (E)) with productivity traits under well-watered (W₁) and water-limited (W₂) regimes was analyzed using 32 public cotton cultivars/bred lines in two field experiments conducted during the normal cotton growing seasons 2003 and 2004. Seed cotton yield (SCY) and biological yield (BY) were markedly affected under W₂ regime in all cultivars except the outstanding performance of CIM-1100 and RH-510 proving their superiority to other cultivars in drought tolerance. Conversely, FH-901, FH-634, and FH-2000 were high yielding under W₁ regime; however, exhibited a sharp decline in yield under W₂ regime. A positive correlation between SCY and BY under water stress (r=0.44 in 2003; r=0.69 in 2004) indicates that BY is also a primary determinant of SCY under water stress and genetic improvement of BY under water-limited environment may also improve SCY. P_n, g_s, and E were significantly reduced by water stress. Substantial genotypic variation for gas exchange attributes existed among the cotton cultivars. A positive association (P<0.01) was observed between g_s and E under both regimes in both years indicating the prevalence of stomatal control of transpiration. The positive association (P<0.01) between P_n and g_s in both years in W₂ regime indicates also a major role of stomatal effects in regulating leaf photosynthesis under water-limited conditions. P_n was significantly correlated with SCY (P<0.01) and BY (P<0.05 in 2003; P<0.01 in 2004) in W₂ regime; however, the level of these associations was not significant in W₁ regime. These findings demonstrate that association of P_n with productivity is effective under water-limited environment and may be useful as a selection criterion in breeding programs with the objective of improving drought tolerance and SCY under water-limited environments. Moreover, association between SCY and BY under water stress suggests that genetic improvement of BY under water stress may also improve SCY.     

Differential responses of leaf water-use efficiency and photosynthetic nitrogen-use efficiency to fertilization in Bt-introduced and conventional rice lines

Leaf stomatal conductance (g _s), transpiration rate (E), and light-saturated net photosynthetic rate (P _Nmax) at three developmental stages (tillering stage, jointing-booting stage, and milking stage) and leaf total nitrogen concentration (LTNC) and δ¹³C value at milking stage were measured for a conventional rice line (Minghui 63) and its corresponding Bacillus thuringiensis (Bt)-gene [cry1A (b and c)] introduced line (Bt line) under three fertilizer levels. Compared to conventional line, Bt line showed lower g _s, which was associated with lower P _Nmax and E, but instantaneous water-use efficiency (WUE), measured as the ratio of P _Nmax to E, was higher in the Bt line than in the conventional line, particularly in the jointing-booting stage. However, δ¹³C values were not significantly different across treatments, suggesting that intrinsic water-use efficiency (WUE_in) might be indistinguishable between Bt and conventional lines. LTNC was higher but P _Nmax was lower in Bt line compared to conventional line, resulting in significantly lower photosynthetic nitrogen-use efficiency (PNUE). This might result from the additional cost of producing Bt protein in the Bt line due to the effect of competing nitrogen with photosynthetic machinery. Bt-gene introduction and expression does not significantly change WUE_in but may significantly decrease leaf PNUE. Thus we suggest that Bt rice should be carefully examined in relation to environmental risks (e.g. water-body pollution) before planting commercially.     

Consumptive and non‐consumptive effects of wolf spiders on cotton bollworms

Larvae of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) that survive on genetically modified Bt cotton (Gossypium hirsutum L., Malvaceae) contribute to the risk of widespread resistance to Bt toxins. Current resistance management techniques include pupae busting, which involves deep tilling of the soil to kill overwintering pupae. Unfortunately, pupae busting runs counter to soil and water conserving techniques, such as minimum tillage. This problem could be relieved with biological control methods, whereby predators attack either larvae going to ground to pupate or moths emerging from the ground. We found that the wolf spider Tasmanicosa leuckartii (Thorell) (Araneae: Lycosidae), a common inhabitant of Australian cotton agroecosystems, is an effective predator of H. armigera, attacking and killing most larvae (66%) and emerging moths (77%) in simple laboratory arenas. Tasmanicosa leuckartii also reduced the number of emerging moths by 66% on average in more structurally complex glasshouse arenas. Males, females, and late‐instar juveniles of T. leuckartii were similarly effective. Tasmanicosa leuckartii also imposed non‐consumptive effects on H. armigera, as when a spider was present larvae in the laboratory areas spent less time on the cotton boll and more time on the soil and more mass was lost from the cotton boll. Increased loss of boll mass likely reflects changes in H. armigera foraging behavior induced by the presence of spiders (indirect non‐consumptive effects). Helicoverpa armigera spent more time as pupae when the spider was present in simple laboratory arenas, but not in more complex glasshouse enclosures. Overall, results indicate that T. leuckartii spiders can be effective predators of H. armigera late instars and moths but also suggest that, under some conditions, the presence of spiders could increase the damage to individual cotton bolls.     

Environmental and physiological regulation of transpiration in tropical forest gap species: the influence of boundary layer and hydraulic properties

Environmental and physiological regulation of transpiration were examined in several gap-colonizing shrub and tree species during two consecutive dry seasons in a moist, lowland tropical forest on Barro Colorado Island, Panama. Whole plant transpiration, stomatal and total vapor phase (stomatal + boundary layer) conductance, plant water potential and environmental variables were measured concurrently. This allowed control of transpiration (E) to be partitioned quantitatively between stomatal (g _s) and boundary layer (g _b) conductance and permitted the impact of invividual environmental and physiological variables on stomatal behavior and E to be assessed. Wind speed in treefall gap sites was often below the 0.25 m s^–1 stalling speed of the anemometer used and was rarely above 0.5 m s^–1, resulting in uniformly low g _b (c. 200–300 mmol m^–2 s^–1) among all species studied regardless of leaf size. Stomatal conductance was typically equal to or somewhat greater than g _b. This strongly decoupled E from control by stomata, so that in Miconia argentea a 10% change in g _s when g _s was near its mean value was predicted to yield only a 2.5% change in E. Porometric estimates of E, obtained as the product of g _s and the leaf-bulk air vapor pressure difference (VPD) without taking g _b into account, were up to 300% higher than actual E determined from sap flow measurements. Porometry was thus inadequate as a means of assessing the physiological consequences of stomatal behavior in different gap colonizing species. Stomatal responses to humidity strongly limited the increase in E with increasing evaporative demand. Stomata of all species studied appeared to respond to increasing evaporative demand in the same manner when the leaf surface was selected as the reference point for determination of external vapor pressure and when simultaneous variation of light and leaf-air VPD was taken into account. This result suggests that contrasting stomatal responses to similar leaf-bulk air VPD may be governed as much by the external boundary layer as by intrinsic physiological differences among species. Both E and g _s initially increased sharply with increasing leaf area-specific total hydraulic conductance of the soil/root/leaf pathway (G _t), becoming asymptotic at higher values of G _t. For both E and g _s a unique relationship appeared to describe the response of all species to variations in G _t. The relatively weak correlation observed between g _s and midday leaf water potential suggested that stomatal adjustment to variations in water availability coordinated E with water transport efficiency rather than bulk leaf water status.     

Photosynthesis and Growth Responses of Parthenocissus quinquefolia (L.) Planch to Soil Water Availability

Photosynthesis and growth characteristics of Parthenocissus quinquefolia were measured under differing soil water availability within a pot. Decreased soil moisture significantly reduced the leaf relative water content (RWC) and the above- and below-ground biomass. However, more biomass was allocated to the root than to the leaf. Net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were also significantly decreased but water use efficiency (WUE) was increased. Midday depressions in P _N and g _s were not evident for the well-irrigated plants. With the lower water availability, midday reductions in P _N and g _s were much more marked and the duration of the depression was longer. Additionally, the P _N-irradiance response curves also indicated that water supply affected photosynthesis capacity. The growth and photosynthetic response of P. quinquefolia to water supply indicated that this species could resilient to water availabilities and adapt to Hunshandak conditions very well.     

Physiological changes and growth of micropropagated chile ancho pepper plantlets during acclimatization and post-acclimatization

Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during acclimatization. Plantlets were transferred to ex vitro conditions to study selected physiological changes and growth performance during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM). Chile pepper plantlets became acclimatized within 6 days after transplantation. During this period, physiological adjustments occurred, which were critical for plantlet survival. After initial ex vitro transplanting, plantlets experienced water deficit [leaf wilting and reduced relative water content (RWC)], which corresponded with reduced stomatal conductance (g _s) and transpiration (E), and an increase in stomatal resistance (r _s). Thus, leaf stomata that developed in vitro were functional ex vitro. Because of this stomatal control, plantlets minimized transplant shock, recovered and survived. Prior to transplanting, plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, g _s, E, and A were significantly lower two days after transplanting. However, within 6 days after transplanting, plantlets recovered and became photoautotrophic – attaining high A, g _s, and E. Water use efficiency was initially low during the first days after transplanting, but increased dramatically at the end of the acclimatization period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with increased plantlet growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

转CpTI-Bt基因棉和转Bt基因棉对棉铃虫幼虫存活、生长及营养利用的影响

2000年7月中旬和8月中旬, 分别测定了采自田间的转CpTI-Bt基因双价抗虫棉（SGK321, 以下简称CpTI-Bt棉）和转Bt基因抗虫棉（中30,以下简称Bt棉）对棉铃虫Helicoverpa armigera幼虫存活、生长的影响。结果表明：7月中旬两种转基因抗虫棉抗虫效果均较好,尤其是CpTI-Bt棉棉叶和花瓣对4龄幼虫3天内致死率为92%以上;8月中旬两种转基因棉的抗虫活性均明显降低,且Bt棉的杀虫活性显著低于CpTI-Bt棉,其幼虫死亡率与对照受体棉中16的死亡率之间无显著差异,仅显著抑制了幼虫的生长;石远321(SGK321受体品系)的花瓣具有一定的抗虫活性,可显著降低取食幼虫的体重,甚至造成部分幼虫死亡; CpTI-Bt棉中,花瓣和棉叶的抗虫性明显高于蕾和铃心。对5龄幼虫取食棉铃1日后的营养指标测定结果显示： 两种转基因抗虫棉处理的幼虫相对生长率和相对取食量均显著低于石远321,但两者之间无显著差异; CpTI-Bt棉处理的幼虫近似消化率显著低于石远321和Bt棉,但其食物利用率显著高于石远321和Bt棉。     

施氮方式对转基因棉花Bt蛋白含量及产量的影响

为研究氮肥运筹对棉花叶片、棉蕾和棉铃不同器官中Bt蛋白含量的影响,2009—2010年,以抗虫杂交棉中棉所72为试验材料,在大田条件下进行了不同基肥：花铃肥：盖顶肥施氮比例（分别为0:0.4:0.6、0.2:0.4:0.4、0.4:0.4:0.2、0.6:0.4:0）的试验。结果表明,施氮方式对棉花不同器官中Bt蛋白含量有明显影响。总体表现为随着氮肥前移,棉花幼嫩器官中Bt蛋白含量呈明显增加的趋势,而老熟器官中Bt蛋白含量呈明显降低的趋势。施氮方式对棉花幼嫩器官中Bt蛋白含量的影响比老熟器官明显,尤其是对幼嫩叶片Bt蛋白含量的影响大于幼小的棉蕾和棉铃器官。抗虫棉采用基肥：花铃肥：盖顶肥为0.4:0.4:0.2的施氮方式,总体能提高前中期棉花器官Bt蛋白的含量,有利于提高其抗虫性能;减少后期棉花器官Bt蛋白的含量,减轻对环境的压力;而且比其余3种施氮方式的籽棉产量和皮棉产量分别增加4.15%—11.24％、3.73%—12.01%。     

Reducing boll weevil populations by clipping terminal buds and removing abscised fruiting bodies

Cotton pests damaging fruiting bodies (squares and young bolls) are difficult to control and their damage results in direct yield loss. Small growers, with low technological inputs, represent a large portion of cotton growers worldwide comprising more than 76 countries; they rely mainly on cultural practices to counteract pest attack in their crops. Boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), oviposition involves puncturing cotton squares and young bolls, causing abscission. We examined the impact on boll weevil population of collecting abscised cotton fruiting bodies and clipping plant terminals at 50% boll maturation in the field during two cotton‐growing seasons and under field cage conditions. Greatest numbers of damaged squares occurred ca. 117 days after planting and clipped plants resulted in reduction of abscised structures and adult boll weevils compared with non‐clipped plants, irrespective of cotton variety. Damaged young bolls were found ca. 128 days after planting in 2009 and 2011, but clipping had no effect. Numbers of boll weevils found in plants of the varieties BRS 201 and BRS Rubi (both in 2009) and BRS Rubi (in 2011) were, respectively, 13‐, 17‐, and 20‐fold greater when clipping plus collecting abscised fruiting bodies were not practiced. Furthermore, the average percentage of the boll weevil parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae) emerging from abscised and collected structures was similar between clipped and non‐clipped plant terminals in both seasons. Clipping plant terminals did not result in yield reduction and reduced adult boll weevil production. Collecting abscised reproductive structures, clipping plant terminals, and using both practices together reduced boll weevil populations by as much as 63, 57, and 79%, respectively, in cage trials. Thus, these practices cause significant impact on boll weevil populations and are feasible of adoption, especially for smallholder cotton growers.     

Sublethal effects of malathion on boll weevil (Coleoptera: Curculionidae) fecundity when maintained on cotton squares or artificial diet

Mated 3‐day‐old female boll weevils, Anthonomus grandis grandis Boheman, reared from field‐infested cotton (Gossypium hirsutum L.) squares were topically treated with an estimated LD₅₀ of malathion (2 μg) to assess its effects on fecundity, oviposition, and body fat condition. Two different food sources, cotton squares and artificial diet, were assessed in malathion‐treated and nontreated (control) weevils. The LD₅₀ caused ～50% mortality in the square‐fed malathion treatment, but the artificial diet‐fed malathion‐treated weevils were less susceptible. LD₅₀ survivors fed on the squares produced ≥ 9 times more chorionated eggs in the ovaries and oviposited ≥ 19‐fold more than survivors fed artificial diet, regardless of the malathion treatment. Boll weevils that survived a 2 μg LD₅₀ malathion and also fed squares were ～4.5‐fold leaner than diet‐fed weevils. Our findings demonstrate that non‐resistant boll weevils surviving a sublethal dose of malathion will reproduce without any delay or significant loss in fecundity, and the food source for which boll weevils are maintained when conducting these assays will directly affect the results. The significance of these findings and how they are related to the final stages of eradicating the boll weevil from the US are discussed.     

Abscisic Acid and cutout in cotton

A decline in growth, flowering, and boll (fruit) retention is referred to as cutout in cotton (Gossypium hirsutum L.). Fruit load affects cutout, possibly through hormonal effects. Experiments were conducted to test the hypothesis that fruits are a source of abscisic acid (ABA) that moves into fruiting branches and growing points where it inhibits growth, flowering, and boll retention. Removal of the flower or young boll at the first node of fruiting branches did not decrease the ABA content of fruiting branches or the abscission zone at the second node. Effects on ABA content of the boll at the second node varied. In one field test, ABA content of bolls at the second node decreased with successive harvests as bolls were removed from first node positions of several fruiting branches. Thus, the effect was cumulative and was not limited to individual branches. Removal of the flower or boll at the first node increased boll retention at the second node. Removal of all flowers during the first 3 weeks of flowering delayed the decreases in growth, flowering, and boll retention that occurred as fruit load increased. But, the ABA content of fruiting branches and mainstem apices was not decreased by early defruiting and did not increase with increasing fruit load. The results do not support the hypothesis that fruits are a source of ABA that moves into fruiting branches and growing points where it then inhibits growth, flowering, and boll retention.     

花铃期干旱和渍水对棉铃碳水化合物含量的影响及其与棉铃生物量累积的关系

在池栽条件下,以美棉33B为材料,研究花铃期干旱、渍水7 d和渍水14 d处理对棉铃碳水化合物含量的影响及其与生物量累积的关系.结果表明: 干旱处理对下部果枝棉铃铃壳碳水化合物含量的影响较小,降低了中部铃壳碳水化合物含量;干旱处理上部铃壳和渍水处理铃壳可溶性糖、淀粉含量增加,蔗糖含量先降后增,且随渍水持续期延长变幅增大,蔗糖外运受阻加重.与铃壳相比,花铃期干旱和渍水处理对棉籽碳水化合物含量的影响较小.干旱和渍水7 d处理中部果枝棉铃生物量快速增长起始期提前但历时短,下部和上部棉铃生物量累积最大增长速率降低;渍水14 d处理不同果枝部位棉铃生物量累积最大增长速率均降低.相关分析表明,棉铃生物量及其最大增长速率与铃壳可溶性糖和蔗糖含量关系密切.因此,花铃期干旱和渍水影响棉铃蔗糖外运,改变棉铃生物量累积特性,是棉铃生物量降低的原因.
     

Daily irrigation attenuates xylem abscisic acid concentration and increases leaf water potential of Pelargonium × hortorum compared with infrequent irrigation

The physiological response of plants to different irrigation frequencies may affect plant growth and water use efficiency (WUE; defined as shoot biomass/cumulative irrigation). Glasshouse‐grown, containerized Pelargonium × hortorum BullsEye plants were irrigated either daily at 100% of plant evapotranspiration (ET) (well‐watered; WW), or at 50% ET applied either daily [frequent deficit irrigation (FDI)] or cumulatively every 4 days [infrequent deficit irrigation (IDI)], for 24 days. Both FDI and IDI applied the same irrigation volume. Xylem sap was collected from the leaves, and stomatal conductance (g_s) and leaf water potential (Ψ_leaf) measured every 2 days. As soil moisture decreased, g_s decreased similarly under both FDI and IDI throughout the experiment. Ψ_leaf was maintained under IDI and increased under FDI. Leaf xylem abscisic acid (ABA) concentrations ([X‐ABA]_leaf) increased as soil moisture decreased under both IDI and FDI, and was strongly correlated with decreased g_s, but [X‐ABA]_leaf was attenuated under FDI throughout the experiment (at the same level of soil moisture as IDI plants). These physiological changes corresponded with differences in plant production. Both FDI and IDI decreased growth compared with WW plants, and by the end of the experiment, FDI plants also had a greater shoot fresh weight (18%) than IDI plants. Although both IDI and FDI had higher WUE than WW plants during the first 10 days of the experiment (when biomass did not differ between treatments), the deficit irrigation treatments had lower WUE than WW plants in the latter stages when growth was limited. Thus, ABA‐induced stomatal closure may not always translate to increased WUE (at the whole plant level) if vegetative growth shows a similar sensitivity to soil drying, and growers must adapt their irrigation scheduling according to crop requirements.