Project Title:  Anthracnose Stalk Rot Resistance from Exotic Maize Germplasm

Justification:

Anthracnose stalk rot (ASR), caused by Colletotrichum graminicola (Ces.) G.W. Wils., causes stalk rot problems and contributes to increased lodging in New York and throughout many U.S. maize-producing areas.  The only economically feasible control of ASR is through resistant varieties and cultural practices that reduce disease incidence.  Recent research has focused on exotic sources for improved ASR resistance, given the limited resistance available in temperate maize germplasm.  This project aims to develop new maize inbreds with excellent resistance to ASR (derived from the tropical germplasm sources used) and good agronomic quality, yield potential, and temperate adaptation (derived from the proprietary temperate inbreds crossed to the exotic populations).

General Objective:

To develop temperate-adapted inbreds with both anthracnose stalk rot resistance and good yield potential from GEM germplasm.

Specific Objectives for Current Project Year:

1) Evaluate finished inbreds and their testcrosses for anthracnose stalk rot resistance and testcrosses for yield potential to choose GEM-derived inbreds for release.

2) Form a population from the best non-stiff stalk inbreds from this project to initiate stalk rot resistance and yield selection.

3) Initiate stalk rot resistance and yield selection in two 75% temperate:25% tropical GEM populations that have good stalk rot resistance and have shown desirable traits in other GEM projects.

Back to Top

Materials and Methods:

Objective 1:  The results described herein represent the latest year of a multi-year inbred development effort.  Results of 1995 per se evaluations were used to select five 75% temperate : 25% exotic populations with potential for anthracnose stalk rot resistance.  Results of 1996 testcross yield evaluations of these populations were used to select the four with the best yield potential.  For each of these four populations, 50 S1 ears were grown out ear-to-row in summer 1997.  Eight plants per family were self-pollinated, injected with approximately 500,000 conidia/plant of Colletotrichum graminicola, and selected for anthracnose stalk rot resistance by splitting and rating the lowermost eight stalk internodes at harvest.  In 1998, selected S2 ears were grown out ear-to-row for another cycle of inbreeding and selection for resistance, and were testcrossed.  For the S3 to the S5 generations (1999 through 2001), selected ears were grown out ear-to-row for inbreeding and selection for resistance and testcrosses from the families that gave rise to these selections were evaluated in yield trials in three New York locations.  Yield and resistance data were used for selection.  In summer 2002, S5 and S6 progenies were planted out ear-to-row for sib increase and testcrossing.  Twenty-seven lines and testcrosses of each to two testers (one public line cross and one Holden’s tester) were planted in two replications at Aurora NY in summer 2003 for stalk rot evaluation as described above.  Most of these testcrosses also had sufficient seed for yield evaluation at three New York locations. These same studies were repeated in summer 2004 and 2005 for all the progenies where seed supply was adequate.  Final 2005 yield plots have just been harvested and final stalk rot ratings are still being taken, so data analysis and interpretation from the 2005 season is yet to be done. 

Objective 2:  Population development was initiated from the best new non-stiff stalk inbreds developed through Objective 1 by making all possible F1 crosses among seven GEM-derived inbreds from three different GEM populations (three from FS8B(T):N1802 and two each from AR01150:N0406 and GOQUEEN:N1603).  The resulting F1s were sent to a winter nursery in Florida where they will be random mated.

Objective 3:  Seed was requested for two 75% temperate : 25% tropical GEM populations (CH05015:N1204 and UR10001:N1702) that performed well in our original anthracnose evaluations in 1995 and have proven useful for other traits (CH05015 has shown promise for yield potential and aflatoxin resistance and UR10001 has shown promise for yield potential and corn borer resistance).  From each population, 150 seeds were sown at high density (about 40,000 plants/acre) and individual plants with good nick and reasonable flowering date were self pollinated to generate S1 families for initial anthracnose stalk rot screening in 2006.

Back to Top

Progress to Date:

Objective 1:

Populations selected based on per se anthracnose stalk rot resistance (evaluated in 1995) and testcross yield potential (evaluated in 1996) were FS8B(T):N1802, CH04030:S0906, AR01150:N0406, and GOQUEEN:N1603.  From these populations, a total of 27 lines were selected based on per se anthracnose stalk rot resistance and testcross yield potential.  Of these, 18 remained in testing through 2004 and 14 looked promising enough to include in seed increases in the 2005 nursery while they were being tested for a final year. 

Data from 2003 and 2004 for the stiff stalk-related lines are presented in Table 1 (those for which relatively complete data is available) and Table 2 (the testcrosses for which yield data was missing from one or more environments).  In all cases, the values for commercial hybrid checks are derived from exactly the same set of environments for which the experimental testcross data is derived, so check values vary from table to table because different numbers and set of environments are included.  Inbreds are listed in Table 1 in order of their stalk rot ratings, from most to least resistant.  Inbred number 253 appears to have the best per se resistance among this group of materials.  Testcross hybrid ratings do not closely parallel the inbred ratings, suggesting non-additive contributions to resistance.  Inbreds 250 and 254 gave excellent resistance in combinations with the RD6501/RD6502 tester.  In general, the RD6501/RD6502 testcrosses were more resistant, higher yielding, higher grain moisture, and more susceptible to lodging than the LH176/LH177 testcrosses.  The stiff stalk-derived GEM inbreds are generally not as highly resistant as the non-stiff stalk-derived inbreds we have developed (see Table 3), but inbreds 195, 250, 253, and 254 appear to have potential for anthracnose stalk rot resistance per se and in hybrid combination and reasonable yield potential.

For the non-stiff stalk-related inbreds, derived from three different GEM populations, data are presented in Table 3.  We have had some difficulty producing seed of some of these inbreds and their testcrosses, and were unable to make testcrosses with LH198 for 2004 testing.  Thus, the data in Table 3 includes two years for B73/CD1 testcrosses but only one year for LH198 testcrosses, and a number of gaps where testcross seed was unavailable or had poor germination.  (The 2003 growing season was so cold and wet that we had general germination problems with all the later season lines in our nursery, which includes the GEM materials and their testers.)  The per se and testcross stalk rot resistance of many of these non-stiff stalk-related inbreds looks very good.FS8B(T):N1802 has yielded the largest number of promising inbreds and three lines from this population (inbreds 222, 259, and 263) appear to have reasonable yield potential as well.  Line 266 from AR01150:N0406 also looks like it has both good per se and testcross stalk rot resistance and reasonable yield potential.

Yield data from 2005 trials has been collected and the last stalk rot ratings are still being done at this point.  These data will be analyzed and summarized in order to make inbred release decisions.

Objective 2:

All possible crosses were made among the lines chosen to contribute to the new non-stiff stalk GEM-related synthetic.  The goal of this effort is to allow recombination among a diverse group of the most promising non-stiff stalk inbreds derived from our GEM work to date, and thus be able to extract a new set of inbreds with excellent stalk rot resistance and improved yield potential and standability.  The lines included in this new synthetic are FS8B(T):N1802 derived inbreds 212, 215, 222, 259, and 263;  AR01150:N0406 derived lines 218 and 26;  and GOQUEEN:N1603 lines 233 and 239.

Objective 3:

We initiated selfing in the two selected GEM populations (CH05015:N1204 and UR10001:N1702).  Due to a prolonged cold, dry period immediately after planting our breeding nursery, germination was not good, and the stands in this material were compounded by it falling into a low spot in the field where soil conditions were even worse than average.  Since we got fewer self pollinations than we had hoped for (about 25-30 in each population rather than 50+), we sent additional seed of both populations to our winter nursery to make more S1 families.  These will be planted out next season to begin anthracnose stalk rot screening.

Back to Top

Summary of Accomplishments:

The major accomplishment for this project to date is the development of advanced breeding lines (nearly finished inbreds) that are showing strong resistance to anthracnose stalk rot.  Resistance in the best of these materials is comparable to that available in currently released U.S. inbreds.  Simultaneous selection for agronomic performance has identified the better fraction of these resistant selections in terms of yield, maturity, and standability.  A few lines have emerged that appear to have good resistance, both per se and in testcrosses, and good yield potential and agronomic quality.  The best of them will be released in 2006.

 

Table 1.  Anthracnose stalk rot (ASR) resistance ratings for inbreds derived from GEM stiff stalk-related population and ASR ratings and yield data for their testcross hybrids in 2003 and 2004.*