mln workshop: breeding for maize lethal necrosis -- b das
TRANSCRIPT
Breeding for MLN tolerance CIMMYT Africa
Biswanath Das, Yoseph Beyene, Stephen Mugo, Manje Gowde, Dan Makumbi, Mike Olsen and BM Prasanna
MLN Diagnostic Workshop, Naivasha 17th to 19th March 2015
CIMMYT’s Collaborative Global Maize Program (GMP)
GMP Focus: • Maize Breeding for the tropics where maize is an important food crop
CIMMYT’s MISSION: To sustainably increase the productivity of maize and wheat systems to ensure global food security and reduce poverty.
30,000 accessions in the CIMMYT genebank –enormous source of genetic diversity.
CIMMYTNARS
GMP Target TraitsAbiotic Stress • Drought • Poor soil fertility/N• Heat• Acid soils• Waterlogging
Biotic Stress • Diseases (Turcicum, GLS, Maize Lethal Necrosis, MSV, Ear rots)• Insects (Stemborers, post harvest pests (weevils, grain borers) • Striga (parasitic weed)
Nutrition (QPM, VitA)• Host R is just one
component of an IPM system
Varieties are screened for all traits during the breeding process
Breeding and Variety Development
Phenotyping
Elite Variety Evaluation
Commercialization
Release
How we workCIMMYT, IITA, NARS
CIMMYT, IITA, NARS, Private Sector
CIMMYT, Private Sector, NARS, NGOs
Regulatory Bodies, Private Sector/NARS
Private Sector/NARS
• Maize is different to many crops due to a vibrant seed sector (120 firms in Africa)• CIMMYT does not release varieties • Most hybrids are released by SMEs and MNCs, OPVs by NARS• It can take over 10 years from variety development to commercialization
Phenotypingnetwork for:• Drought• Low N• Striga• MSV• MLN
Artificial infestation of maize plants with stem borer eggs
Past Experience: Stemborers
Measuring Leaf Toughness
R Traits
Leaf damage score (1-9) Tunnel length Exit holes
Busseola fusca and Chilo partellus
Striga work initiated in 1998• 2.3 million ha affected by Striga in Africa
(AATF, 2006) resulting in yield losses between 20 and 80%
• Imidazolinone (herbicide) resistance exists naturally in maize and is easy to work with (single gene)
• Conversion of maize inbreds and hybrids to Imidazolinone resistant (IR) versions + herbicide seed coating formulation (BASF)
In 2013/14 3 OPVs and 5 hybrids released in Kenya and Tanzania
Genetic gains - MSVGrain yield
(t ha-1)Anthesis date
(d)ASI
Location Country Year Mean h Mean h Mean hHarare Zimbabwe 2012 5.21 0.79 76.1 0.89 -0.1 0.51Harare Zimbabwe 2013 7.21 0.72 71.7 0.91 0.6 0.37Harare Zimbabwe 2013 6.93 0.92 71.6 0.98 0.5 0.41
Combined 6.45 0.82 73.1 0.83 0.3 0.72
Estimated gains in tolerance to MSV: 141.3 kg ha-1 yr-1
(2.2% yr-1)
Maize Lethal Necrosis (MLN)
Symptoms: Severe mottling of leaves, dead heart, stunted growth (shortened internode distance), leaf necrosis and barren ears.
Why is MLN devastating maize in EA?
• MCMV is new to the region and the current strain is particularly aggressive
• Widespread cultivation of susceptible germplasm that has never been screened for MCMV
• Very favourable agronomic and environmental conditions
What has the EA maize breeding community done?
1. Artificial inoculation and screening protocols established in collaboration with OSU
2. MLN screening facility established at KALRO-Naivasha
3. Thousands of maize accessions screened for MLN by public and private sector
4. Promising hybrids have been submitted and recommended for fast track release in Kenya
Germplasm Evaluation by CIMMYT
Screening Year Location Entries Total Rows1st Screening Nov-12
Olerai and SunripeFarm 2,636 5,272
2ndScreening Jun-13
Oleria and Marula Farm 8,021 16,042
3rd Screening March-April 2014 KALRO Naivasha
19,53939,078
4th Screening October 2014 to Date KALRO Naivasha
15,32220,356
TOTAL 45,518 80,748
Approximately 65% of entries are inbreds.
Type of Germplasm Evaluated
• Diverse Inbred lines from CIMMYT’s Global Maize Program and collaborators (OSU and KU)
• Experimental and elite hybrids
• DH populations
• Biparental mapping populations
• Assocation mapping sets
Updates on Screening (2013)
May 2014
Breeding Approach
• Evaluation of existing elite hybrids for immediate recommendation (eg WE1101)
• Identification of donor inbreds• Formation of new hybrid combinations using
donor inbreds• Recycling donor inbreds (pedigree, BC, DH) for
development of new lines and next generation hybrid combinations
Inbred screening
Bad News: Close to 90% of materials susceptible
Good News: 10% of materials shows some tolerance
Bad News: Current elite CMLs collapse against MLN
CML442 CML443 CML448 CML444
CML395
Most widely used CML in existing commercial hybrids
Good News: Genetic Variation Exists
Severity Score Frequency in IMAS-AM panel
Distribution of Score frequencies indicates disease pressure is satisfactory and genetic progress can be made
Inbred line Kernel color Heterotic Group Max. MLN severity score
Disease response rating
CLRCY039 Y B 2.0 RCLYN261 Y A 2.0 RCLRCY034 Y B 2.0 RCKDHL120552 W A 2.3 MRCKDHL120161 W B 2.4 MRCKDHL120668 W B 2.4 MRCKDHL120664 W B 2.4 MRCML494 W B 2.5 MRTZMI730* W B 2.5 MRCKDHL120918 W B 2.5 MRCML550 W B 2.6 MRCML543 (CKL05003) W B 2.7 MRCKDHL120671 W B 2.7 MRCLA106 Y B 2.7 MRCKSBL10205 W AB 2.7 MRCKSBL10194 W AB 2.8 MRCML535 (CLA105) Y B 2.8 MRCKSBL10060 W A 2.9 MRCKDHL121310 W B 3.0 MRDTPYC9-F46-1-2-1-2-B Y A 3.0 MRCKDHL0500 W B 3.0 MR
Table 1. Responses of selected CIMMYT maize inbred lines to artificial inoculation with MLN at Narok and Naivasha in Kenya (2014)
Sources of Resistance are not ideal
CLRCY039CLRCY034
• Resistance is coming from unadapted tropical lowland sources from Latin America, SE Asia and from temperate germplasm from the USA.
• Most resistant lines tend to be yellow – there appears to be strong linkage between Y-1 and MCMV resistance.
Line Development Strategy• Resistant lines used directly in pedigree and DH breeding
pipelines: Over 900 pedigree starts made in 2014 alone. (F3)
• Resistant yellow lines are being converted to white versions by BC. Time consuming as yellow is dominant and MCMV R appears to be closely linked to Y1. (F2)
• Elite CMLs (eg CML442, CML444, CML312) are being converted to MLN-tolerant versions through phenotypic selection and MAS (BC2)
• DH can speed up the process and increase likelihood of fixing the right gene combinations (DH lines obtained)
• We know there are loci for SCMV R on Chr3 and Chr10. Relatively little is known about MCMV R.
Over 7,000 hybrids screened in 2014. Around 30 are showing promise for MLN and other traits. These have been submitted for release
HYBRID/PRODUCT DEVELOPMENT
MLN Scores (1-5)Entry Pedigree 1 3 4
13 CKH10085 1.8 2.6 2.518 CML78/P300C5S1B-2-3-2#-#1-2-B*7-#-B 1.8 2.0 2.6
5 CKIR12014 2.1 2.0 2.74 CKIR12010 2.1 2.9 2.8
28 CKH10773 1.7 3.2 2.92 CKIR11027 1.9 2.8 3.0
29 H513 3.3 3.9 4.430 H520 3.3 3.6 3.631 H614 3.2 3.2 3.332 H624 2.8 3.2 3.533 WH403 3.3 3.6 4.634 WH507 3.6 3.3 3.935 WH505 3.0 3.5 4.036 PAN691 3.6 3.9 3.837 PANM419 3.2 3.5 4.438 DUMA43 3.5 3.9 4.739 PHB30G19 2.1 3.1 3.340 DK8031 3.7 4.0 4.7
Mean 2.5 3.3 3.6LSD 0.85 0.74 0.88CV 17 11 12
Heritability 0.79 0.71 0.71
Results of hybrid re-validation trials at two locations
Commercial check
CKDHH0995
Promising pre-commercial hybrids with MLN tolerance
NUE Hybrids in NPT in East Africa
Hybrids submitted for release on basis of Low N + MLN scores below 3
Commercial Checks
New Hybrids are showing up to a 1 point (20%) improvement compared to checks
Hybrid Status MLN1 MLN2 MLN3
CKH10769Released in Uganda and Kenya
2014 2.9 3.0 3.2
CKH10767Released in Uganda and Kenya
2014 2.5 3.5 3.5
CHMLND0086 (CKH12600)
Recommended for release in UG in 2015. Top on-farm in TZ. 2.5 2.8 2.8
CKH12603Recommended for release in UG
in 2015 2.9 2.8 2.7
CKH12607Recommended for release in TZ
in 2015 2.7 3.0 3.0CKH12601 2.7 3.0 3.5CKH12613 2.4 2.7 3.0CKH12616 2nd year of NPT in Kenya 2.5 2.7 2.7
CKH126022nd year of NPT in Kenya and seed
scale-up underway 2.9 3.0 3.0NPT Check 3.7 3.7 3.7
Hybrids in NPT in EA
Expanding Phenotyping Capacity
• Heavy emphasis on MLN site at Naivasha• Disease pressure is high• Elevation (1900m) means most germplasm is
evaluated outside natural ecology
• There is a need for natural hotspot sites in the target agro-ecology
• Requirements: disease presence, data collection, agro-ecological parameters
MLN Network
Site Country Inoculation Method
Capacity Planting Season
Location
Naivasha Kenya Artificial Inoculation 16 ha April & OctLatitude: -0.68197734Longitude: 36.39519367Elevation: 1911m
Babati Tanzania Natural Hotspot 2 ha MarchLatitude: -4.20963602Longitude: 35.73990726Elevation: 1378m
Karama Rwanda Natural Hotspot 5 ha MarchLatitude: -2.24102797Longitude: 29.64548721Elevation: 1613m
Thank You