BREEDING FOR RESISTANCE TO BACTERIAL BLIGHT OF COTTON IN RELATION TO RACES OF THE PATHOGEN

Abstract                                                                         Back to Table of contents

Bacterial blight of cotton incited by Xanthomonas campestris pv malvacearum (Xcm) occurs in most cotton producing regions of the world.  Bacterial blight causes a 1% yield loss annually in the USA, and more than 50% loss during epidemics in Africa.  Currently 19 races of Xcm are recognized in the USA.  A shift in races of the pathogen has recently occurred in Texas, from USA races 1, 2 and 7 to the most virulent race 18.  In Africa, new virulent isolates (HVS) of the pathogen have evolved, with HV1 being highly virulent.  At least 22 major genes (B) for resistance to Xcm have been reported.  The majority of these genes are partially to completely dominant for resistance.  Additive and digenic interactions were also reported.  Single resistance genes confer resistance to a few races (vertical resistance), but are vulnerable to the other races of the pathogen.  Thus, different combinations of single B genes and modifiers are important to obtain a stable source of horizontal resistance.  Immunity to all USA races of the pathogen conferred by the B2B3BSm gene combination has been stable for 22 years in the USA. Resistance to the HV1 isolate has been obtained in Africa.   Selection must be made utilizing a compatible race mixture of the pathogen, including virulent races to identify gene combinations that give broad spectrum resistance to many races.  Recurrent selection and the backcross methods have been used to develop horizontal resistance to all races of the pathogen.  Resistant cultivars will reduce disease incidence and severity, and control bacterial blight.

Conclusions

Cotton pathologists and breeders have made considerable advances in breeding for resistance to the bacterial blight pathogen.  High resistance is available in several cultivars throughout the world.  For example, Siokras in Australia; Barakat, Bar, and Baras in the Sudan; Allen, Uk74, UK71, Albar, Reba B50 in East and Central Africa; BJR-734 in India, and the Tamcot cultivars and MAR germplasm in the USA have been developed for resistance to the bacterial blight pathogen.

Continued focus and progress should be made worldwide  to develop cotton cultivars with high and stable resistance to the virulent races of Xanthomonas campestris pv malvacearum.  We agree with Painter’s (1951) view that resistant cultivars are not a panacea for all pest problems. The use of resistant cultivars alone should not be expected to control pests under all conditions or in all locations where the crop may be grown.  Resistant cultivars should be used in concert in integrated pest management  (IPM) programs, which may also include minimal use of pesticides, cultural management, and biological control.  Cotton cultivars with resistance to insects and pathogens, high yielding ability, earliness and improved fiber quality provide the cornerstone for a successful and profitable production system.

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AGRONOMIC MANAGEMENT OF EXTRA FINE COTTON FOR HIGHER GRADES IN EGYPT

Introduction                                                               Back to Table of contents

Egyptian cotton is the major cash crop of Egypt.  It is the main item affecting the Egyptian economy.  Over two million people are dependent on it for their livelihood.  Cotton is mainly used for clothing.  Its oil and oil seed cake are two by-products used by man and animal.

Cotton growing started in Egypt in 1820, when a Frenchman, Monsieur Jumel, discovered a kind of fine cotton that was planted in an orchard.  Mohamed Ali Pasha, the founder of Modern Egypt imported some Sea Island and Brazilian cotton seeds between 1832 and 1865.  We believe these three varieties are the origin of Egyptian cotton.

Cotton growing and production was monopolized by the government up to 1840, when it was liberated by Said Pasha, the governor of Egypt at that time; since then it greatly flourished.  Strangely enough we realized that the same applies now.  Thirty years after nationalization of the cotton trade, it seems the only way for cotton to regain its glory is to go back to free trade.

….More in the downloadable file

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INDUCTION OF SOMATIC EMBRYOGENESIS IN A RANGE OF COTTON CULTIVARS

Abstract                                                                         Back to Table of contents

Diverse genotypes of cotton Gossypium hirsutum L. were evaluated for their capacity to form callus formation and for induction of somatic embryogenesis.  Callus cultures were evaluated from hypocotyl, mesocotyl and cotyledonary leaf explants, harvested from in-vitro germinated seedlings.  For callus induction eight different initiation media were tested.  Maintenance medium for all the cultures was the same, used initially for callusing.

After a series of sub-cultures, calli were transferred into embryo initiation medium which consist of Murashige and Skoog (1962) basal medium, Gamborg B5 vitamins, glucose (3%) and agar (0.6%).  After several weeks, calli were screened for the presence of embryonic units.  The embryogenic tissue were isolated and sub-cultured on embryo-proliferation medium (Finer, 1988).  After 4-6 weekly sub-culture, three different cell lines were obtained from the hypocotyl derived callus in cv PKV 081, which was previously identified as being highly embryogenic.  Microscopic preparation showed the presence of somatic embryos in various stages of development.  In one cell line derived from Coker 417-68, differentiation of a shoot was observed.

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THE AUSTRALIAN WILD SPECIES OF GOSSYPIUM

Abstract                                                                         Back to Table of contents

Of the 50 species of Gossypium, 17 are endemic to Australia.  These plants are classified in three sections, Sturtia, Hibiscoidea and Grandicalyx, in the endemic subgenus Sturtia.  The first two sections are relatively well‑known through the species G. sturtianum and G. australe, respectively.  Section Grandicalyx, although more restricted in distribution than the other two, contains the greatest taxic diversity.  Historically, this section is poorly known.  Of its 12 species, six were first recognised and described only within the last 11 years.  The twelfth species was collected and recognised for the first time in 1993.  The wild Australian species share a feature unique in the genus, i.e. a terpenoid‑glanded plant but functionally glandless embryo.

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RISK OF ESCAPE OF TRANSGENES FROM COTTON INTO NATURAL POPULATIONS OF AUSTRALIAN GOSSYPIUM SPECIES

Abstract                                                                         Back to Table of contents

Two endemic species of wild cotton, Gossypium sturtianum and G. australe, occur near the eastern Australian cotton growing regions. These species can be crossed artificially with cotton (G. hirsutum) and experimental doubling the chromosome number of the hybrid overcomes its sterility. It is therefore remotely possible that the same processes might occur in nature, and transgenes from genetically engineered cultivars might leak into natural populations. To evaluate the risk further, we compared the distribution of the wild species with the Australian cotton growing area, and examined their natural breeding system. A survey of herbarium records showed that only a small portion of the distribution of these wild species approaches the cropping area. Isozyme variation in samples from two populations each of G. sturtianum and G. australe gave estimates of outcrossing of about 4% and 40% respectively. The major barriers to gene escape into the wild species via pollen is the remoteness of most of their populations and the unlikelihood and the sterility of interspecific hybridization. Predominant self-pollination in G. sturtianum thus forms an additional barrier, and reduces still further the risk of their escape from the crop into wild populations.

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VOLATILE TERPENES AND TERPENOID ALDEHYDES IN AUSTRALIAN-GROWN GOSSYPIUM HIRSUTUM L. CULTIVARS AND LINES

Abstract                                                                         Back to Table of contents

Volatile terpenes were assayed in sixteen Gossypium hirsutum L. genotypes, seven of which were also analysed for terpenoid aldehydes. Consistent with previous studies, the major volatile terpenes detected were trans-b-caryophyllene, b-bisabolol, a-humulene, myrcene, g-bisabolene, trans-b-ocimene, a-pinene and b-pinene. Across genotypes, relative percentages of major individual terpenes were similar within, but differed widely between the leaf, square and boll coat. The boll coat was relatively rich in trans-b-ocimene and heliocides H1 and H4. These heliocides together accounted for approximately 50-80% of total terpenoid aldehydes in the boll coat. This finding may have significance for the development of cultivars resistant to Helicoverpa  spp. in Australia.

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MECHANISMS OF DISEASE RESISTANCE IN GOSSYPIUM SPECIES AND VARIATION IN VERTICILLIUM DAHLIAE

Introduction                                                                Back to Table of contents

Studies on Verticillium wilt of cotton have concentrated on host resistance to the pathogen and on genetic variation and mechanisms of virulence in Verticillium dahliae.  The resistance of cotton to V. dahliae depends on a number of anatomical and chemical characteristics that occur both constitutively and as active defense responses.  Terpenoid phytoalexins and condensed tannins appear to be especially important in defense reactions. Resistance in cultivars correlates with the concentration of tannin in leaves, the rate of phytoalexin synthesis in xylem vessels in response to infection, and the toxicity of the phytoalexins and tannins to V. dahliae.  Enzymes that appear to have critical roles in regulating terpenoid and tannin synthesis have been characterized, and partial genes coding for these enzymes have been cloned.  Strategies for manipulation of these genes and for introduction of foreign genes from other malvaceous plants to improve cotton resistance to wilt are being developed.  Vegetative compatibility (V-C) tests and isozyme analyses have been used to show that there are four genetically isolated populations (V-C groups) within the species V. dahliae, and that each V-C group has at least two subgroups.  The V-C groups and subgroups vary in geographical occurrence, virulence to cotton and other crops, and sensitivity to fungicides.  The severe defoliating form of Verticillium wilt found in the southwestern USA and in Peru is caused by isolates in the V-C 1A subgroup, whereas wilt in Europe and Asia is caused by isolates in the V-C 2 group.  Wilt in Australia is incited by isolates in the V-C 4B subgroup.  Isolates in the V-C 1A group show unique resistance to the antibiotic sanguinarine and have the ability to induce large accumulations of ammonium ions in cotton leaf tissues.  Identifying the specific V-C groups responsible for wilts in a given field and geographical area should allow better recommendations for disease control measures…

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HYBRID COTTON RESULTS AND PROSPECTS

Abstract                                                                         Back to Table of contents

Hybrid 4 ushered in the era of hybrid cotton in India in the 1970s.  Hybrids both intra and interspecific now occupy about 28% of the cotton area and contribute about 42% of production of the country.  Inspired by the unique success of hybrid cotton in India, researchers in many cotton growing countries intensified their research on hybrid cotton.  A sizeable area is devoted to F1 and F2 hybrids in China.  In many other countries F1 or F2 hybrids are a distinct possibility in the near future.  The high cost of seed, which is a deterrent for the development or spread of hybrids can be overcome by exploiting male sterile systems coupled with bee pollination.  For hybrids to be successful they should be very high yielding, early maturing, moderately resistant to biotic and abiotic stresses with good fibre properties and above all, they have to be more profitable than varieties to attract farmers to grow them.

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QUALITY ASSESSMENT FOR BREEDING EGYPTIAN HIGH QUALITY COTTON VARIETIES

Abstract                                                                         Back to Table of contents

The cotton breeding program in Egypt has developed over a long time.  Strong emphasis has always been put on quality and a good deal of improvement  with  yield potential and agronomic characters.

Methods of quality measurement and  evaluation  of  strains tested in the breeding  program  have  developed  through  three distinct stages: (i) in the  early  days, quality  assessment depended mainly on the graders skilled judgment and later on fiber length and fineness,  (ii)  as  from  1936,  assessment depended on yarn strength supported by fiber length and fineness and (iii) as from the mid 1960s, a  new  system  has been developed that takes into account several important quality parameters including: fiber,  length,  fineness  and   maturity, strength  and  elongation  and  yarn  strength, neppiness  and regularity. The system is based on setting up guide‑line scales for each of the four quality categories of Egyptian cotton.   It is concluded that such  systems  are  helpful  but  it  is  the skilled judgement  of  experienced technologists  that  counts  in giving the breeder the support he needs.

Conclusion

From the extensive experience gained through more than a quarter  century  of  involvement  with  the  Egyptian  cotton  breeding program, it could be concluded that in dealing with high quality ELS and LS cottons, breeding  offers  many  valuable  opportunities  for improvement.  Depending on systems based on  guide‑lines  scales  or other approaches for selection for quality is  undoubtedly  helpful. However, in all cases, what is really needed is the skilled judgment of experienced technologists who can use knowledge and vision of the future requirements of the cotton users to  make the appropriate interpretation of the various  quality  measurements and gives the breeder the effective support he needs.  Breeders  and technologists should work in close collaboration in order to achieve the goals of cotton breeding programs.

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IMPERIAL VALLEY COTTON FIELDS SURVEYED WITH PLANT MAPPING

Abstract                                                                         Back to Table of contents

We introduced the University of California Plant Mapping Program to growers in the Imperial Valley for the first time for the 1993 cotton season.  Because the equations used in the program were derived from data collected in the San Joaquin Valley for Acala varieties, many potential users questioned the validity of applying the program to Upland cotton fields growing in the low desert (i.e. Imperial Valley).  They wanted to know if the program could make accurate predictions for varieties other than Acalas in an environment other than the San Joaquin.  Could they trust their management decisions to a program developed from another region’s database?

In order to address these concerns and to help convince the growers of the value of plant mapping, we collected both in-season and final plant map data from thirty Imperial Valley cotton fields during the 1993 season. Height to node ratios vs. age (as number of nodes) for Imperial Valley plants followed the same pattern, but were slightly lower than, the curve for San Joaquin fields.  Some fields came closer to the line representing the San Joaquin database than others.  Nodes above white flower values from Imperial Valley fields followed the same relationship to days after first flower as the San Joaquin fields.  Growers actively making management decisions with the aid of the programs picked over 2242 kg lint/ha.  Those not guiding their decisions brought in less than 1121 kg lint/ha.  We determined two factors critical to good cotton production in the low desert:  timing of early season irrigation and early retention of first position fruits.  We conclude that the UC Plant Mapping Programs served as useful guides in an area quite different from the San Joaquin.

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