Trans. Br. mycol. Soc. 76 (3) 367-370 (1981) Printed in Great Britain

PRELIMINARY SURVEY OF COTTON FLOWER MYCOFLORAFROM SUDAN

By MAHGOUB H. ABDALLA* AND NAGAT M. EL-TAYEB

Department of Botany, Faculty of Science, University of Khartoum, Sudan

Fungal colonization of cotton bolls takes place between the first and second week followingflower opening under Sudanese field conditions. Aspergillus spp, constitute the pioneer cottonflower contaminants.

Moulds isolated during the 7 weeks that followed flower opening were A.fiavus, A.fumi-gatus, A. nidulans, A. niger, A. terreus, Chaetomium spp., Curvularia sp., Helminthosporiumsp., Rhizopus stolonifer and Thielavia sp. Capsules (pericarp and locks) were more heavilycolonized than accessory floral parts (pedicel and epicalyx). Fungal invasion is promotedby damage due to bollworm infestation.

The production of cotton, the crop of first eco-nomic importance to the Sudan, has more thantripled during the last two decades (300000 tonsyearly). However, apart from phytopathologicalwork, research on the mycofiora of cotton and itspossible implication in cotton fibre deteriorationis deficient.

As a natural product 94 % of the cotton fibre'sweight is composed of cellulose. Other constituentslike wax, organic acids, pectin, nitrogenous sub-stances, non-cellulosic polysaccharides and un-identified substances make up the remaining 6 %(Sadov, Korchagin & Matetsky, 1973). Hencecotton fibre is readily colonizable by moulds andeven under the dry weather conditions of theSudan the damage caused by moulds is significantparticularly when xerophytic fungi, such as Asper-gillus spp. are involved. Apart from fibre destruc-tion and decrease in tensile strength the productionof undesirable pigments and toxic secretions alsocause economic loss (Galloway, 1935; Bollenbacher& Marsh, 1954).

The ovary contents become the main target forfungal infection of pre- as well as mature cotton inthe field (Wiles, 1963; Caquil & Ranney, 1967;Roncardori, 1967, 1969). Saprophytic fungal colon-ization of cotton boll may be facilitated by thesystemic spread of pathogens, such as Fusariumspp, (McCarter, Roncardori & Crawford, 1970),invasion through insect-made pores (Mostafa,1959), or via decaying floral parts, bracts, etc.(Balk, 1958; Henderson & Christensen, 1961;Pinckard, 1964; Marsh, 1965).

Losses of cotton crop have also been attributed

* Present address: Botany and MicrobiologyDepartment, Facultyof Science, Universityof Kuwait,State of Kuwait.

to boll rot caused by moulds such as Diplodia sp.,Alternaria sp., Nigrospora sp., Aspergillus niger andAi flaous (Marsh & Kerr, 1961) which occur ascontaminants and may subsequently lead to bollrot when high relative humidity prevails at thetime of boll opening. The decrease of fibrestrength as well as length, following fungal in-fection of lint, has been confirmed by Stands,Fiori & Groves (1962).

The present work was aimed at contributing toknowledge of the incidence of fungi associatedwith sound and worm-infested cotton bolls, recordof which is lacking under Sudanese conditions.

MATERIALS AND METHODS

Three localities (Matorab, Wad Shafie and WadSulfab) representing the main cotton growing areasin Gezira Central Sudan were chosen for thepresent study.

The variety of cotton (Gossypium barbadenseL.)employed was the long and extra long staple'Barakat', sown in summer (between July andAugust). Random sampling, from inside the field,to avoid the edge effect, was made during twoseasons (1975 to 1976 and 1976 to 1977) whenplants were 10 to 12 internodes high. Samples ofninety flowers (per season), classified as youngflowers (1 to 7 days post-flower opening) de-veloping to fully mature bolls (3 to 7 weeks post-flower opening), were collected. The bolls werefurther classified as sound and worm-damaged andexamined for their mycoflora.

Isolation

The young and the withered flowers were aseptic-ally dissected, following Roncardori (1969), into

0007-1536/81/2828-7350 $01.00 © 1981 The British Mycological Society

Table 1. Mean percentage mould infection of youngcotton flowers (1 to 7 days post-opening, all samplingareas)

Ai fia uus, A. terreus, R. stolonifer and A. nidu/answere highly prevalent in all samples surveyed. Itwas noticed that the pericarp was the main targetof infection and that it harboured the bulk of fungalcontaminants when compared with either themycoflora of the epicalyx or locks, except inworm-blemished bolls from Matorab where thefrequency of occurrence of lock contaminants in-creased by 26'9 % over that of the capsule. Theminor fungi listed in Table 2 were present onsamples from all three localities except Aspergillusfumigatus Fres. which was recorded in low fre-quency only on worm-damaged samples from theMatorab and Helminthosporium sp, which appearedonly on material from W. Sulfab. A noticeable en-hancement in the incidence of A. niger, Chaeto-mium sp., and Thielavia sp, was recorded in theseventh week of flower development when lintreached maturity.

DISCUSSION

The results show that A. niger was the principalpioneer contaminant of the floral segments fol-lowed by A. nidulans and then Rhizopus stolonifer,Although the ovary was extremely tiny (1 to 7 dayspost-flower opening) , it was the main target ofmould invasion while the calyx and epicalyx ex-hibited nearly the same incidence of infection.

A. niger remained dominant in mature flowerswhile the frequency of isolation of A. nidulans de-creased in sound ovaries. In tests for celluloseclearing ability A.flavus, A . nidu/ans, A. niger andA. terreus were rated as highly cellulolytic byAbdalla & El-Tayeb (1981). The isolation of twomore cellulolytic genera, Chaetomium and Thiel-avia, from 3 to 7 week-old ovaries may indicatethe early establishment of mould-damaged linteven before boll opening. According to the litera-ture Thielavia has not been previously isolatedfrom cotton fibre, but Thie/aviopsis has beenreported repeatedly (Bagga & Ranney, 1969).

Although Fusarium oxysporum Schlecht. f. sp.uasinfectum (Atk.) Snyder & Hansen, the cotton

Epicalyx Calyx Ovary

94'4 95'S 10061'1 5°'9 40'012'2 23'0 54'114'4 5'3 18'96'7 2'2 0

31'1 27'7 76'7

A spergillus nigerA. nidulansAi fiauusA. terreusCurvularia sp.Rhizopus stolonifer

368 Colton flower mycoflora

three parts, the epicalyx (or flower bract), calyxand the whole tiny ovary. The developing and thefully mature bolls were segregated into pedicel andepicalyx, and capsule. The latter was furtherseparated into the pericarp or ovary wall and locks(locular contents of the capsule consisting of lintand seeds).

The floral segments were serially washed in 5 to8 fresh changes of 20 em" sterile water, surfacesterilized in 1 % sodium hypochlorite in 95 %ethanol (1 :5 vIv) (Roncardori, 1969) for 12 minand subsequently rinsed in two fresh changes ofsterile water . The washed floral parts were thenseparately plated out onto Ohio Agricultural Ex-perimental Station's medium (containing 50 mgstreptomycin sulphate+50 mg chloromycetin per1-1 of medium) (Kaufman, Williams & Summer,1963) and incubated at room temperature (32 to36°C) for 5 days. The frequency of mould occur-rence and the percentage infection of floral seg-ments were then calculated.

RESULTS

Cotton flowers, under Sudanese field conditions,may become highly contaminated with mouldsduring the first week following flower opening(Table 1). All examined floral parts yielded mainlysaprophytic fungi. Arranged in descending orderof dominance the following fungi were recordedfrom the epicalyx, calyx and ovary, Aspergillusniger Van Tiegh., A. nidulans (Eidam) Winter,Rhizopus stolonifer (Ehrenb. ex Fr.) Lind, A.flavus Lk ex Fr., A. terreus Thom. Curvularia sp,was the only pathogen isolated (from the accessoryfloral parts only) at this stage of flower develop-ment. The young ovary yielded many contamin-ants while the epicalyx and the calyx supportedrelatively fewer fungal species.

The development of ovaries into bolls wasaccompanied by bollworm infestation which wassevere during the 1975 to 1976 season. In allsampling areas, worm-blemished 3- to 7-week-old ovaries exhibited the highest mould con-tamination compared with sound bolls collectedfrom the same field. Repre sentative results fromW. Sulfab data are presented in Table 2. The myco-flora of the epicalyx and the pelicel was less thanthat of either pericarp or locks except in worm-damaged samples from W. Shafie. The fungalflora of damaged capsule components (pericarpand locks) was highest in W. Shafie samples fol-lowed by W. Sulfab and then Matorab. The fungiisolated from 3- to 7-week-old flowers were vari-ably distributed as far as the sampling areas andfloral structures examined were concerned. Ar-ranged in descending order of dominance, A. niger,

M. H. Abdalla and M. L. El-Tayeb

Table 2. Percentage infection and frequency of mould occurrence (in parentheses) in floral segments of3 to 7 week-old worm-infested (BW) and sound (8) cotton bolls

W. Sulfab"--

Floral segments* BW S'---- -, ,----- "-- ---....

Fungus a b c a b c

Aspergillus fiavus 13'3 26'7 16'7 3'3 13'3 23'3(4) (8) (5) (1) (4) (7)

A. fumigatus ° ° ° ° ° °A. nidulans ° 5° ° 3'3 3'3 °

(15) (1) (1)A. niger 100 100 90 70 100 86'7

(3°) (3°) (27) (23) (30) (27)A. terreus 10 13'3 33'3 3'3 6'7 3'3

(3) (4) (10) (1) (2) (1)Chaetomium spp. 0 ° 6'7 10 ° °

(2) (3)Curvularia sp. ° 10 13'3 ° ° 10

(3) (4) (3)Helminthosporium sp. 6'6 ° 0 ° 0 0

(1)Rhizopus sp. 6'7 26'7 3°'0 ° 0 0

(2) (8) (9)Thielavia sp. 13'3 13'3 0 13'3 0 10

(4) (4) (4) (3)Total frequency ofoccurrence:

Flower segment 44 72 57 33 37 41-y '------y

Capsule+locks 129 78

Whole flower 173 111

* Floral segments: a, epicalyx-l-pedicel; b, pericarp; c, locks.

wilt agent (Ibrahim, 1966) and Macrophominaphaseolina (syn. Sclerotium bataticola), the causalagent of black nuts (Abdalla, 1974) are highlydominant in Gezira soils, they were not isolatedfrom cotton flowers during the present investi-gation. Helminthosporium sp. was ranked as arare contaminant in spite of the abundance ofthese species in the Gezira (El Amin & Abdalla,1980).

The accessory floral parts, namely the pedicel andepicalyx, supported relatively fewer fungi thaneither the pericarp or locks. Although the de-veloping fibres in the locks are rich in solublecarbohydrates, in addition to cellulose, they sup-ported fewer fungi than the pericarp. The myco-flora of the peri carp therefore seems to play animportant role in mould development on thecapsule and ultimately fibre biodeterioration.Cotton bolls became particularly susceptible tofungal invasion when they were insect-pored.Rhizopus stolonifer colonization was especially

associated with boll-worm damage and this ob-servation agrees with Mostafa (1959) that boll rotis due to R. nigricans (syn. R. stolonifer) invasionsubsequent to worm damage in Egypt. Ashworth,Rice, McMeans & Brown (1971) noticed that thequality of lint deteriorated as a result of mouldinfection following worm damage.

It may be assumed that the fungal propagulesgain access into the capsular and subsequentlylocular tissues, between one to two weeks after theflower opens, through the stomata covering theboll surface (Baher & Pinckard, 1970).

This paper is dedicated to the memory of thelate Ibrahim Ahmed Nasr, M.Sco, Ph.D., ChiefPlant Pathologist, Guneid Sugar Cane Estate,Sudan.

Facilities offered during the preparation of themanuscript by the Department of Botany andMicrobiology, University of Kuwait are gratefullyacknowledged.

Cottonflower mycoflora

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37°

(Received for publication 17 January 1980)