Protocols for Phenotyping Segregating
Maize Gene Bank Accessions
Martha C. Willcox1*; Juan Burgueño1; Armando Guadarrama1; Daniel Chepetla1; Enrique Rodríguez1; Dan Jeffers1; Ricardo Ernesto Preciado2; Arturo Terrón2; ; Humberto Leonel
Vallejo2; María Esther Rivas3; George Mahuku1 Heriberto Torres 4; Fernando González 4; Francisco Parra 4; Marco Oropeza 4; Rosemary Shrestha1; Peter Wenzl1; Sarah Hearne1.
1. CIMMYT, Int. 2. Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias; 3. BIDA Sem; 4. Pioneer de México; . * [email protected]
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INTRODUCTION Maize Landraces have a high level of heterogeneity and
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Standar deviation
heterozygosity between and within gene bank accessions. Maize is naturally open
pollinated and farmer selection, over millennium, has produced groupings for
specific morphological, environmental and use characteristics that are identifiable
as races of maize. To adequately characterize such heterogeneous materials it is
necessary to evaluate the levels of segregation within accessions for the traits
evaluated. Traits such as plant and ear heights, and disease resistance ratings, are
not adequately characterized by measuring a single plant or by the row median.
Data must be taken on an individual plant basis with the number of individual plants
measured being sufficient to capture the segregation within the accession for the
trait desired, thus providing a measurement of the variability between plants in the
same accession. With this in mind, new protocols were developed to obtain precise
and accurate data from a plant basis that allows calculation of internal variability.
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Average
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Relationship between standard deviation and the
average of stalk rot rating taken by plant..
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By plant
Stalk splitting method for
rating stalk damage
caused by Acremonium
strictum and Fusarium
sp.
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Accesion testcrosses in color by tester,
hybrid checks in black
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By plot
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Relationship between Fusarium Stalk Scale taken by plant and
fusarium stalk rot scale taken by plot.
METHODOLOGY The Seeds of Discovery Initiative, whose goal is to
open the bottle neck between maize and wheat germplasm banks and
breeding programs, has genotyped a single plant per accession of the
4000+ accessions in the CIMMYT Maize Genebank’s Breeder’s Core
Collection. The single plant genotyped per accession was crossed onto 10
plants of a CIMMYT hybrid of the same environmental adaptation to
produce an accession/testcross for phenotypic. We have in several trials
taken data both, by plot and by individual plant. The traits were foliar
disease scores for Tar Spot resistance; stalk rot scale (Fusarium and
Acremonium strictum). Stalk Rot Scale = (number of affected plants/total
number of plants) x stalk rot score of affected plants (1-5 with 5 being
most damaged).
The effect of the tester is overriding the effect of the accession in the
stalk rot rating by plot. The stalk rot scale taken on a plant basis allows
more discernment of the accession’s resistance.
RESULTADOS
Correlation between data by plot and by plant.
Fusarium intensity
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Fusarium scale
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Tar spot scale
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Segregation of ear color within accesion testcrosses indicates
the segregation seen within these materials.
CONCLUSIONS
Overall results are similar in both approaches, by plant or by plot. Taking data by plant is more time consuming than in a plot basis, but it is the
only way in which we can effectively estimate the variability intra-accession and improve the scale of measurement for correlation with genotypic
data.