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.     

Transmission of cotton seed and boll rotting bacteria by the southern green stink bug (Nezara viridula L.)

AIMS: To determine the ability of the southern green stink bug (SGSB) (Nezara viridula L.) to transmit Pantoea agglomerans into cotton (Gossypium hirsutum) bolls. METHODS AND RESULTS: An SGSB laboratory colony was kept on fresh green beans. A P. agglomerans variant resistant to rifampicin (Rif) (strain Sc 1-R) was used as the opportunistic cotton pathogen. Adult insects were individually provided green beans that were sterilized and then soaked in either sterile water or in a suspension of strain Sc 1-R. Insects were individually caged with an unopened greenhouse-grown cotton boll. After 2 days, live SGSB were collected, surfaced sterilized, ground, serially diluted, and then plated on nonselective media and media amended with Rif. Exterior and interior evidence of feeding on bolls was recorded 2 weeks after exposure to insects. Seed and lint tissue were harvested, ground, serially diluted, and then plated on media with and without Rif. Bacteria were recovered on nonselective media from all insects, and from seed and lint with signs of insect feeding at concentrations ranging from 10(2) to 10(9) CFU g(-1) tissue. The Sc 1-R strain was isolated only from insects exposed to the marked strain and from seed and lint of respective bolls showing signs of insect feeding. Evidence of insect feeding on the exterior wall of the carpel was not always apparent (47%), whereas feeding was always observed (100%) on the interior wall in association with bacterial infections of seed and lint. CONCLUSIONS: Nezara viridula readily ingested the opportunistic P. agglomerans strain Sc 1-R and transmitted it into unopened cotton bolls. Infections by the transmitted Sc 1-R strain caused rotting of the entire locule that masked internal carpel wounds incurred by insect feeding. Bacteria were recovered from penetration points by insects not exposed to the pathogen, but locule damage was limited to the area surrounding the feeding site (c. 3 mm). SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study that demonstrates the ability of SGSB to acquire and transmit plant pathogenic bacteria into cotton bolls.     

Potential for <Emphasis Type="Italic">Nezara</Emphasis><Emphasis Type="Italic">viridula</Emphasis> (Hemiptera: Pentatomidae) to Transmit Bacterial and Fungal Pathogens into Cotton Bolls

Recently, we showed that the southern green stink bug (SGSB), Nezara viridula (L.), can transmit Pantoea agglomerans (Ewing and Fife), an opportunistic bacterium, into green cotton bolls resulting in plant disease. Here, we hypothesized that our established model could be used to determine if the SGSB was a general, non-discriminate vector by using two other opportunistic bacterial pathogens of bolls (Pantoea ananatis [Serano] and Klebsiella pneumoniae [Schroeter]) and the known fungal pathogen Nematospora coryli (Peglion). Variants of P. ananatis (strain Pa-1R) and K. pneumoniae (strain Kp 5-1R) selected for rifampicin (Rif) resistance were used as bacterial opportunists. N. coryli was detected only from laboratory-reared SGSB directly exposed to the fungus. Both Pa-1R and Kp 5-1R were recovered from SGSB previously provided a contaminated food source (2 days), sterile food (5 days), and then harvested after being caged on bolls (2 days) at levels reaching 10³ and 10⁴ colony forming units (cfus) per insect, respectively. However, bolls caged with insects infected with Pa-1R or Kp 5-1R and with evidence of feeding did not become diseased nor were either opportunists detected from boll tissues. Insects infected with N. coryli transmitted the pathogen, which resulted in diseased bolls and fungi concentrations reached 10⁶ cfus/g locule tissue at 2 weeks following the caging period. Notably, each of the three pathogens independently caused boll disease when mechanically inoculated using a needle puncture. Generally, these results suggest that cotton pathogen acquisition by the SGSB was not sufficient to determine whether the insects were disease vectors of the opportunists.     

Fungi associated with boll and lint rot of cotton in Southern Khorasan province of Iran

During surveys of cotton fields since 2009 in the Southern Khorasan province of Iran, symptomatic samples with lint and boll rot disease signs were collected and cultured on potato dextrose, malt extract agar and PARPH media. Several fungal isolates were obtained and identified. Among them, we found Penicillium expansum which to our knowledge is reported as a new pathogen of cotton worldwide; Fusarium semitectum and Nigrospora oryzae (associated to mite Siteroptes sp.) were also recorded as lint or boll rot pathogens for the first time from Iran. Disease symptoms and fungal characteristics of Exserohilum rostratum, which has been reported briefly as a new causal agent of boll and lint rot disease, are illustrated and presented. In addition, Aspergillus niger and Rhizopus spp. were also isolated frequently from lint parts of cotton prior to harvesting. There was a positive correlation between disease occurrence and spiny cotton bollworm damage. The pathogenicity test was characterised by inoculating the attached and detached bolls of cotton plants.     

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.     

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.
     

苗期遮荫对棉花产量与品质形成的影响

为揭示棉麦两熟共生期遮荫对棉花产量与品质形成的影响。在棉花苗期利用模拟棉麦两熟共生期遮荫的方法进行了研究。结果表明,遮荫对棉铃形成的影响因果枝,果节部位而异,遮荫有利于棉株下（1-3果枝）,中（4-6果枝）,上（7-9果枝）部果枝内围（1-2果节）铃的形成,对外围（≥3果节）尤其顶部果枝（≥10果枝）外围铃形成不利,从而决定铃重也随果枝,果节部位相应地变化,但遮荫对单株平均铃重的影响畔 小,变遮荫棉花籽棉产量而论,下,中部果枝的内围铃籽棉产量高于常规棉,在上,顶部果枝则相反,各部位果枝外围铃的籽棉产量均低于常规棉,遮荫棉花内,外围铃分布为1：0.36(常规棉为1：0.58),产量分布为1：0.42(常规棉为1：0.72)。苗期遮荫对棉纤维,棉籽品质性状的影响也主要在顶部果枝和上部果枝外围铃,综合分析遮荫棉花产量与品质的形成,棉花苗期耐遮荫性品种间存在差异。在本研究中以中9418耐遮荫性最强,中棉所19和春矮早次之。     

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.     

Transmission of Alternaria macrospora in Cotton Seeds

Alternaria macrospora was isolated from seeds only after the natural opening of the bolls and exposure of seeds to an environment in which the fungus was present. The fungus lacks the ability to penetrate the boll wall and reach the seed site. Attempts to isolate the pathogen from seeds of immature bolls at different developmental stages failed. Internal infection by slow injection resulted in seed infection and partial shedding of the injected plant parts which was high in buds and decreased with the ripening to mature bolls. Severity of seed infection was not dependent on either inoculum level, boll physiological age or even if the boll itself was not diseased. Infection of flowers under field conditions caused flower shedding. Naturally infected seeds or inoculated seeds with inoculum levels of 100 spores/ml and above resulted in diseased cotyledons, the incidence of which was, for inoculated seeds, positively correlated with inoculum level. A small difference was observed between cultivars in susceptibility to artificial inoculation at the cotyledon stage. A. macrospora survived on commercial cotton seeds and on post-season plants left growing at the field edges. Survival in plant debris under field conditions was minimal and may only have a minor effect on field reinfestation.     

Bacteria on closed-boll and commercially harvested cotton.

The bacterial content of specially treated cottons used by other investigators to test human pulmonary responses to cotton dust was examined. Cotton from Lubbock, Tex. and Stoneville, Miss. were either (i) harvested by machine and handled as commercial bale cotton, (ii) harvested as closed bolls with bracts intact and opened under special conditions, (iii) harvested as closed bolls, with bracts being removed and opened under special conditions, or (iv) harvested by (stoneville only). Bacillus spp. were isolated from all samples and predominated in cotton from Stoneville. Enterobacter agglomerans was isolated from all but one sample, the Stoneville closed-boll bract-removed cotton, and predominated in Lubbock samples. Aerogenic and anaerogenic biogroups of E. agglomerans were isolated; only aerogenic strain b of E. agglomerans was present in samples from both locations. Klebsiella ozaenae and K. pneumoniae were isolated only from Lubbock samples. Cotton from Lubbock yielded 100 to 1,000 times more bacteria, both total and gram negative, than did comparably treated cotton from Stoneville. Thus, differences in growing and processing conditions at the two locations were associated with large differences in the bacterial content of the cotton, but harvesting green bolls and removing bracts had little effect. The bacterial content of Stoneville washed cotton, and it paralleled the differences reported (Boehlecke et al., Am. Rev. Respir, Dis. 123:152, 1981) in pulmonary function responses when subjects were exposed to dust (0.6 mg/m3) from these two cottons. Levels of gram-negative and total bacteria on all samples were comparable to those previously reported for field-weathered cottons from various locations throughout the world.     

BACTERIAL BOLL ROT OF COTTON (XANTHOMONAS MALVACEARUM (E. F. SMITH) DOWSON)

Two inoculation techniques were compared for their value in assessing resistance of cotton to bacterial boll rot. In the first method, bacterial suspensions were applied with a fine brush to the outsides of young bolls immediately after corolla drop. In the second, suspensions were inoculated into the wall tissue of bolls 3–4 weeks old with a fine needle. The second method is the simpler and produces infections in all weather conditions; other advantages are that bolls are inoculated after the period of natural shedding and the circular lesions are easily measured, but a disadvantage compared with the brush method is that the puncture method does not satisfactorily indicate damage to the lint.
Results from the two methods of inoculation suggest that resistance lies in some component of the boll-wall tissue that affects bacterial growth and not in a physical factor that prevents the bacteria entering the boll. Variability in resistance occurs in local strains of cotton, and this could probably be exploited to give high resistance without the need of a large crossing programme to introduce new genes.     

Genome sequence of Pantoea sp. strain Sc 1, an opportunistic cotton pathogen

Pantoea is comprised of a broad spectrum of species, including plant pathogens. Here, we provide an annotated genome sequence of Pantoea sp. strain Sc 1, which was isolated from a diseased cotton boll. This research provides the first genome sequence of a bona fide Pantoea sp. insect-vectored cotton pathogen.     

The degree of susceptibility of nectary-inoculated cotton flowers and bolls to subsequent seed infection by Aspergillus flavus is determined at or before anthesis

In greenhouse and field studies, cotton (Gossypium hirsutum L.) flowers were inoculated with Aspergillus flavus at the involucral nectaries. Bolls developing from early-season flowers had significantly higher percentages of A. flavus-infected seed than did bolls from flowers formed later in the season. Seeds from bolls inoculated 2 weeks after anthesis had the same infection levels as those from flowers inoculated at anthesis. These results indicate that early-season flowers are predisposed to A. flavus infection and that the degree of susceptibility at anthesis is retained through early boll development.     

The occurrence of Aspergillus flavus in vegetative tissue of cotton plants and its relation to seed infection

Twenty-seven mature cotton bolls with Aspergillus flavus Link colonies naturally occurring on the surface of the boll or lint were collected in the field in Arizona along with their subtending stems and peduncles. Bolls inoculated through the carpel wall 30 days after anthesis were allowed to mature in the field and were collected in the same manner. The seed and stem and peduncle sections of each boll were surface-sterilized, plated on agar media and observed for A. flavus. Seventy-eight percent of the naturally contaminated bolls with A. flavus in the seed also had the fungus in the stem and peduncle, whereas only 31% of the naturally contaminated bolls with no A. flavus in the seed had the fungus in the stem or peduncle. This difference was significant (P=0.0125), indicating a positive relationship between seed infection and stem and peduncle infection. All of the bolls inoculated through the carpel wall had A. flavus in the seed, but only 11% of the stem and peduncle sections were infected, indicating that the fungus does not readily grow downward from the boll into the supporting stem or peduncle.This unidirectional pattern of movement (upward) was further substantiated in greenhouse experiments where cotton seedlings were inoculated at the cotyledonary leaf scar with A. flavus and plants were sequentially harvested, surface sterilized and plated. Aspergillus flavus was isolated from the cotyledonary leaf scar, flower buds, developing bolls, and stem sections in the upper portion of the plant. It was never isolated from roots or stem sections below the cotyledonary node, again indicating that the fungus does not readily move downward through the plant.     

Relationships of abscised cotton fruit to boll weevil (Coleoptera: Curculionidae) feeding, oviposition, and development

Abscised cotton, Gossypium hirsutum L., fruit in field plots planted at different times were examined to assess adult boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), use of squares and bolls during 2002 and 2003 in the Lower Rio Grande Valley of Texas. Although boll abscission is not necessarily related to infestation, generally more bolls abscised than squares and abundances of fallen bolls were not related to the planting date treatments. During 2003, fallen squares were most abundant in the late-planted treatment. Although large squares (5.5-8-mm-diameter) on the plant are preferred for boll weevil oviposition, diameter of abscised squares is not a reliable measurement because of shrinkage resulting from desiccation and larval feeding. Fallen feeding-punctured squares and bolls were most abundant in late plantings but differences between fallen feeding-punctured squares versus fallen feeding-punctured bolls were found in only one treatment in 2003. During the same year, fallen oviposition-punctured squares were more numerous in the late-planted treatment than in the earlier treatments. Treatment effects were not found on numbers of oviposition-punctured bolls, but fallen oviposition-punctured squares were more common than bolls in the late-planted treatment compared with earlier treatments each year. Dead weevil eggs, larvae, and pupae inside fallen fruit were few and planting date treatment effects were not detected. Living third instars and pupae were more abundant in fallen squares of the late-planted treatment than in the earlier treatments and bolls of all three treatments. This study shows that fallen squares in late-planted cotton contribute more to adult boll weevil populations than bolls, or squares of earlier plantings.     

Line x tester analysis for fixed effect model in cotton (Gossypium hirsutum L.)

Summary The data from an experiment in cotton consisting of three testers and 12 lines selected deliberately have been analysed. The investigation showed higher specific combining ability variance for yield of seed cotton and number of bolls, indicating the predominance of non-additive gene action. Of parental lines, H777 was found to possess high g.c.a. effects for seed cotton yield, number of bolls and number of sympodes. Parent H842 contributed only for boll weight, whereas H655 was good general combiner for number of monopodes. There appeared to be better chances for increasing the yield by exploiting hybrid vigour for the number of bolls and boll weight. The presence of marked non-additive gene effects, in addition to additive gene effects, indicated the need for exploiting both the fixable and non-fixable components of genetic variance for increasing productivity in cotton.     

The Degree of Susceptibility of Nectary-Inoculated Cotton Flowers and Bolls to Subsequent Seed Infection by Aspergillus flavus Is Determined at or before Anthesis

In greenhouse and field studies, cotton (Gossypium hirsutum L.) flowers were inoculated with Aspergillus flavus at the involucral nectaries. Bolls developing from early-season flowers had significantly higher percentages of A. flavus-infected seed than did bolls from flowers formed later in the season. Seeds from bolls inoculated 2 weeks after anthesis had the same infection levels as those from flowers inoculated at anthesis. These results indicate that early-season flowers are predisposed to A. flavus infection and that the degree of susceptibility at anthesis is retained through early boll development.     

First Report of Rhizoctonia solani AG‐7 on Cotton in Egypt

Eighty‐two isolates of Rhizoctonia solani were recorded from roots of naturally‐infected seedlings of the Egyptian cotton (Gossypium barbadense L.). Anastomosis groups (AGs) of the isolates were determined by using 13 different AGs testers. Three (3.7%) of the isolates were identified as R. solani AG7, while the remaining isolates were belonging to the AG 2‐1, AG4 and AG5. The identification of the three isolates was based on the frequency of the C2 reaction with the AG7 tester isolate. No fusion was observed between AG7 and isolates representing the other 13 AGs. Colonies of AG7 isolates grown on potato dextrose agar (PDA), malt yeast agar (MYA) and melt peptone agar (MPA) were brown to dark brown with aerial mycelium and sclerotia. The isolates had pitted sclerotial clusters and brownish exudates after 21 days of culturing on PDA, but without clear zonation. Pathogenicity test under greenhouse conditions revealed that AG7 caused the common symptoms of damping–off, which included seed rot, lesions on the hypocotyls and root rot.     

Influence of Nezara viridula feeding on cotton yield, fiber quality, and seed germination

The influence of southern green stink bug, Nezara viridula (L.), adults (males and females) and fourth to fifth instars on cotton, Gossypium hirsutum L., boll abscission, seedcotton yield, fiber quality, and seed viability was evaluated in field studies conducted during 2004 and 2005. Cotton bolls representing several age classes ranging from 0-600 heat units were individually infested with a specific gender or life stage of southern green stink bug. Adults and nymphs induced abscission of bolls that accumulated 0-280 heat units after anthesis. Seedcotton yield was significantly lower in bolls infested with adults (males and females) and late instars through approximately 500 heat units after anthesis. Southern green stink bug feeding on bolls significantly affected the physical fiber properties of micronaire (measure of fiber fineness or maturity), strength, uniformity, and fiber length. Discolored cotton lint in the stink bug-infested bolls was more common than in noninfested bolls. Seed germination and development of normal seedlings for seed harvested from stink bug-infested bolls that accumulated < or =500 heat units beyond anthesis were significantly lower compared with noninfested bolls. No significant differences in boll abscission, yield, fiber quality, and seed germination were detected between southern green stink bug males and females or between adults and fourth to fifth instars.     

Distribution and Races of Xanthomonas axonopodis pv. malvacearum on Cotton (Gossypium hirsutum) in Uganda

Surveys in 1995 and 1996 showed that bacterial blight caused by Xanthomonas axonopodis pv. malvacearum occurs throughout the main cotton growing areas of Uganda, causing seedling blight, angular leaf spot and bacterial boll rot. During the vegetative and early fruiting stages of crop growth, severe symptoms of `blackarm' spread from leaves to the stem, causing loss of fruiting branches. A set of Upland cotton cultivars ( Gossypium hirsutum ) were then used to determine the races of the blight bacterium present in Uganda. Many of the isolates induced moderate to severe symptoms on all the test hosts except 101–102B, indicating infection with race 10 or 18. The next most common isolate was race 7. Races 16 and 6 were also identified and 23% of isolates caused symptoms on all the differential cultivars including 101–102B, results indicating the presence of a race of the pathogen which may be the same as that identified in countries neighbouring Uganda and designated as race 20.