Genetic improvement of crop plants Essay
Bananas ( Musa spp.
L ) are one of the most of import fruits in the universe and are grown in many tropical and semitropical countries where they are used as both a basic nutrient ( cooking banana ) and dietetic addendums ( dessert banana ) ( Pillay et al. , 2002 ) . Dessert banana are consumed natural when they are mature ( Pillay et al. , 2002 ) . Beside the beginning of nutrient, other parts of banana, the dry foliages are used for fruit wadding and the green foliages used as home bases for wrapping nutrient ( Pillay et al. , 2002 ) .In most states, sweet banana production is for export trade, and this is comprised mostly of a individual cultivar, ‘Cavendish ‘ ( Becker et al.
, 2000 ) . The Cavendish subgroup is the most important subgroup of comestible bananas ( Ploetz et al. , 2007 ) . They are major export trade goods in Central America, South America, the Caribbean, West Africa, and the Philippines ( Ploetz et al. , 2007 ) .
They comprise over 40 % of comestible bananas that are produced worldwide ( Ploetz et al. , 2007 ) . In equatorial Lowlandss where the ambient temperatures are high, fruits turn greenish-yellow when ripe, although where temperatures are a spot ice chest or when unnaturally ripened, they turn bright yellow ( Ploetz et al. , 2007 ) .Therefore, this harvest betterment program would concentrate on the restraints to production of the Cavendish subgroup.
Taxonomy and Origin
The genus Musa ‘s centre of beginning is in Indochina and Southeast Asia ( Simmonds, 1962 ) .
Banana belongs to the Musaceae household, one of the six households of the order Zingiberales ( Pillay et al. , 2002 ) . The Musaceae comprises of two genera, Musa and Ensete ( Pillay et al. , 2002 ; Ploetz et al. , 2007 ) . Four subdivisions have been recognized in the genus Musa viz. ; Australimusa, Callimusa, Rodochlamys and Eumusa ( Pillay et al.
, 2002 ) . The subdivision Australimusa and Callimusa have a basic set of 10 chromosomes whilst the other two subdivisions have 11 chromosomes ( Pillay et al. , 2002 ; Ploetz et al. , 2007 ) .
Genome Groups in Musa
Domesticated bananas are of course happening loanblends between two wild diploid ( ten = 11 ) M. acuminata Colla. and M. balbisiana Colla whose genomes are designated as A and B severally ( Ploetz et al.
, 2007 ) . Hybridization between races of M. acuminata produced a scope of diploid cultivars ( AA genomes ) ( Pillay et al. , 2002 ; Ploetz et al. , 2007 ) . Diploid AAs produced triploid AAA types by chromosome damages ( Pillay et al. , 2002 ) .
Hybridization between AA diploids and M. balbisiana ( BB ) gave rise to the many AAB and ABB types ( Pillay et al. , 2002 ; Ploetz et al. , 2007 ) . The cultivated triploid AAA genome comprises the sweeter sweet banana whereas the AAB and ABB are starchy cooking types ( Pillay et al.
, 2002 ) . Other genome groups largely merchandises of engendering plans include AAAA, ABBB, AAAB and AABB ( Ploetz et al. , 2007 ) .
The triploid AAA genomes consist of three subgroups viz. ; Cavendish, Gros Michel and Ibota ( Ploetz et al. , 2007 ) .
This subgroup is made up of the undermentioned ringers ; ‘Pisang Masak Hijau ‘ , ‘Grand Nain ‘ , ‘Giant Cavendish ‘ , ‘Dwarf Cavendish ‘ , ‘Double ‘ and ‘Extra Dwarf Cavendish ‘ in falling order of the tallness to which they grow in a given location ( Ploetz et al. , 2007 ) .The subgroup is immune to Panama disease in the western Torrid Zones, but is susceptible to the Black Sigatoka disease, direction of the latter disease is a major disbursal in commercial production, particularly in countries with high rainfall ( Pillay et al.
, 2002 ) . The ringers are similar except for their tallness and features of the clump and fruit ( Ploetz et al. , 2007 ) .
Except ‘Extra Dwarf Cavendish ‘ , all are productive if they are provided with ample fertiliser and H2O ( Ploetz et al. , 2007 ) .
This is the most widely distributed ringer of comestible banana worldwide and it is the shortest used for commercial production since tall ringers Lodge in high air current and hard to reap ( Ploetz et al. , 2007 ) . It bears good-quality fruit, with a long conveyance life if picked at the right adulthood and is good suited for place garden, commercial, and agroforestry cultivation ( Gubbuk et al. , 2004 ; Ploetz et al.
, 2007 ) . Short and compact, it is comparatively cold tolerant ( Ploetz et al. , 2007 ) .
Pest and diseases jobs are increasing of import constrainst ( Pillay et al. , 2002 ) . Black Sigatoka, caused by Mycosphaerella fijiensis Morelet is the major restraint for banana productions ( Pillay et al. , 2002 ) .
This disease causes from 30 to 50 % output decrease and is normally control with monolithic application of man-made antifungals. Yellow Sigatoka ( caused by M. Musicola Leach ) besides causes similar harm ( Pillay et al. , 2002 ) .
Other of import diseases include Banana streak virus, Fusarium wilt, bunchy top virus disease, bacterial wilt and banana mosaic disease ( Pillay et al. , 2002 ) .Plant parasites ( roundworms ) can do harm to banana ensuing in output losingss ( Pillay et al. , 2002 ) .
Other plagues, including Banana weevil can do harm to banana throughout the Torrid Zones ( Pillay et al. , 2002 ) .
Constraints to Improvement
Dwarf Cavendish is a triploid ( 2n = 3x = 33 ) and therefore present several barriers to conventional betterment methods ( Simmonds, 1960 ; Ssebuliba et al. , 2006 ) . By and large characterised by low male and female birthrate that consequences in really low seed output ( less than 1 seed per clump ) and sprouting rates ( less than 1 % ) ( Ortiz and Vuylsteke, 1995 ; Vulsteke et al. , 1993 ) . It takes over a twelvemonth to travel from seed to seed ( Pillay et al. , 2002 ) .
Get the better ofing Constraints
Ploidy Manipulation, birthrate and Seed managing
Conventional traversing methods have been successful in bring forthing inter- and intra-specific loanblends as a consequence of minimising sterility barriers ( Ssebuliba et al. , 2006 ) . Improvement of triploid Musa species has been achieved through traversing 3x landraces with 2x ( diploids ) wild ( Ssebuliba et al. , 2006 ) .Through embryo deliverance and bodily embryogenesis technique banana workss can be regenerated ( Assani et al. , 2001 ) .
Embryo civilization is reported to heighten seed sprouting and intercrossed recovery ( Pillay et al. , 2002 ) . It is possible to obtain embryo sprouting rates of up to 30 % on plant hormone free medium compared to 1 % from direct sowing of seeds in dirt ( Vuylsteke and Swennen, 1992 ; Ortiz and Vuylsteke, 1995 ) . Therefore, in vitro embryo civilization is considered as an built-in constituent of banana-breeding plans ( Pillay et al. , 2002 ) .
However, the success in banana genteelness relies on the designation of female fertile landraces ( Ssebuliba et al. , 2006 ) .
Improvement Plan for Dwarf Cavendish
Aim: To better opposition of Dwarf Cavendish to Black Sigatoka disease.Harmonizing to Ssebuliba et al. , 2006 adequate degrees of opposition against this disease have non been found in the cultivated bananas but have been identified in wild species. Of peculiar involvement is a fertile wild diploid species M. acuminata spp. burmannicoides ‘Calcutta 4 ‘ ( Vuylsteke et al.
, 1993 ) , which is immune to black sigatoka and a figure of other diseases and plagues. ‘Calcutta 4 ‘ with an AA genome composing is one of the primogenitors of comestible bananas and has been used in many genteelness plans to reassign black sigatoka opposition to cultivated bananas ( Swennen and Vuylsteke, 1993 ; Vuylsteke et al. , 1993 ) .Technique: Use Asymmetric Somatic Hybridisation to reassign Black Sigatoka opposition trait from Calcutta 4 to Dwarf Cavendish. Since conventional crossing will take a long clip, labour intensive and jobs with low female birthrate, this technique will assist in overcome this barriers ( Ssebuliba et al. , 2006 ) .
Plant stuffs and civilizations
Disease free embryogenic cell suspensions of the triploid banana ( Musa sp. AAA group ) and non-embryogenic callosity of the diploid banana ( Musa sp.
AA Calcutta 4 ) can be used as the beginning of energids ( Matsumoto et al. , 2002 ) . The embryogenic cell suspension can be obtained from a male blossoming and maintained in a modified MS ( Murashige and Skoog, 1962 ) liquid medium ( Matsumoto et al. , 2002 ) . The non-embryogenic callosity can be induced from a male blossoming tip on a medium consisting of MS ( Matsumoto et al.
, 2002 ) . The induced callosity can be maintained on the modified MS medium without the growing regulators ( Matsumoto et al. , 2002 ) .
Isolation of energids and Cultures
Energids from the cells suspension of Dwarf Cavendish and callosity of Calcutta 4 can be isolated as described antecedently ( Matsumoto and Oka, 1998 ) .
Energids of Dwarf Cavendish can be treated with Indoacetoamide ( IOA ) to forestall cell divisions prior to fusion whilst energids of Calcutta 4 can be treated with soft X raies to demobilize the karyon ( Akagi et al. , 1989 ) . Resistance to Black Sigatoka is contributed through cytoplasmatic genomes and this will assist in the Restoration of the seedless trait of Dwarf Cavendish while keeping it output and fruit quality ( Pillay et al. , 2002 ) .
Asymmetrical merger of Energids and works regeneration
Fusion of the two parental energids can be achieved with chemical ( polyethylene ethanediol PEG ) or electrofusion engineerings.
Methods for protoplast civilization, settlement development and works regeneration as described by Matsumoto and Oka, 1998 can be followed to regenerated workss.
Designation of Asymmetric Somatic Hybrids
Early designation of asymmetric bodily loanblends at R1 phase utilizing molecular markers ( RAPD, SSR, ISSR and RFLP ) have been developed for the two parents and ploidy can be determine to corroborate asymmetric loanblends utilizing flow cytometric ( Matsumoto et al. , 2002 ) .
In vitro Selection for Resistance
Harelimana et Al. ( 1997 ) have demonstrated that it is possible to utilize Mycosphaerella fijiensis toxins for the choice of banana cultivars resistant to Black Leaf Streak in vitro. Therefore, it can be considered as an option for rating at an early phase.
Host Pant Pathogen Surveies
This can be done by seting asymmetric loanblends that will be identified at phase R1 in an experimental secret plan surrounded by extremely susceptible Cavendish cultivar to make an environment that provided sufficient inoculants possible for appraisal of Black sigatoka opposition ( Ortiz and Vuylsteke, 1994 ) . All harvest direction patterns can be used except fungicide application ( Craenen and Ortiz, 1998 ) .
Quantitative Traits for Black Sigatoka opposition
Resistance of single works trait may include: youngest foliage with symptoms, youngest foliage spotted at blossoming, because no leave develops after blooming ( Craenen and Ortiz, 1998 ) . Individual foliage traits may include: incubation clip, development clip, disease development and life span of the foliage ( Craenen and Ortiz, 1998 ) . These traits can be used to develop quantitative trait venue for Black sigatoka opposition ( Ortiz et al. , 1997 ) .
General Quantitative traits
This may include: yearss to blossoming, works tallness at blossoming, fruit filling clip ( yearss from blooming to reap ) , growing rhythm, works girth, entire figure of foliages, clump weight per works, fruit weight, fruit length, fruit girth, hands per clump, fruits per clump, and fruit parthenocarpy traits ( Ortiz et al. , 1997 ) .
Field proving and Selection
Multilocational testing of immune assortments and subsequent release of immune loanblends.Evaluation will be base on the heritable quantitative traits involve in disease opposition ( Ortiz et al. , 1997 ) .
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