THINGS I WORRY ABOUT
CP 65-357, A NEW SUGARCANE VARIETY FOR LOUISIANA!/
H. P. Fanguy
Southern Region, Agricultural Research Service, USDA Houma, Louisiana
ABSTRACT
CP 65-357 is a clone from a cross between CP 52-68 and CP 53-17. The cross was made at Canal Point, Florida, during the 1960 crossing season. It was selected in the clonal stage at Houma, Louisiana.
Results from extensive replicated yield trials indicate CP 65-357 is outstanding in both tons of cane per hectare and kg of sugar per ton of cane. Yield data from multiple-location tests indicate it will be well adapted to all areas and soil types of the Louisiana sugarcane producing area. A major advantage of CP 65-357 is its ability to produce high yields and yet remain erect. Mosaic spread data indicate CP 65-357 is susceptible to mosaic, but limited mosaic yield trials suggest that it is tolerant to the disease. CP 65-357 is also being tested in Florida and Texas to determine whether it is adapted to those areas.
INTRODUCTION
The Louisiana sugarcane industry relies on new and better varieties for its survival. But for the imported POJ varieties, the industry would not have survived the low yields of 1925-26 (1). The POJ varieties, although susceptible to mosaic, were tolerant to the disease and maintained the industry until they were replaced by the Co and mosaic-resistant CP varieties.
The US Sugarcane Field Station at Houma, Louisiana, was established during this critical period of low sugar yields. Personnel at the Houma Station have participated in the testing and release of 31 varieties to the sugar industry. They consisted of 2 Co, 1 NCo, 3 L, and 25 CP varieties (9).
The sugar industry is presently growing 1 NCo variety, 3 L varieties, and several CP varieties.
Hopefully, CP 65-357 will help maintain and increase sugarcane yields obtained from these varieties.
DEVELOPMENT AND TESTING
CP 65-357 was selected and tested under the 3-way agreement by the USDA, the La. Agric. Exp. Sta., and the American Sugar Cane League. CP 65-357 is a clone derived from a cross between CP 52-68 and CP 53-17. The cross was made at Canal Point, Florida, during the 1960-61 crossing season. The variety was selected in the seedling stage and reselected in the clonal stage at the Houma Station over a 5-year period; stalk size, stalk height, sucrose content, and stalk solidness were used as criteria (3). The variety was then tested in nursery and replicated yield trials for 3 years in the infield programs at Houma and the La. Agric. Exp. Sta. in Baton Rouge (10).
Further testing in replicated trials at the multiple USDA and LSU outfield locations (4) took place for 3 years.
CP 65-357 was rated susceptible to mosaic in the infield tests but was nevertheless advanced to the outfield tests because it was outstanding from an agronomic standpoint. Mosaic counts made in the rep- licated outfield plots confirmed its susceptibility (5). CP 65-357 was dropped from the testing and increase program at the meeting of the variety advancement committee in 1970 because of its mosaic susceptibility. Mosaic-resistant varieties L 65-69 and CP 65-350 and moderately resistant varieties CP 66-376 and L 66-48 were all promising at that time. Although CP 65-357 was dropped in 1970, it had been planted in replicated outfield plots at 13 locations in 1969. The 1970 growing season was good and lodging was considerable when unusually heavy rains fell in Sept. and Oct. CP 65-357 had unusually good erectness under these conditions at all the outfield locations, whereas the mosaic resistant varieties L 65-69 and CP 65-350 were badly lodged.
Breaux (2) found it difficult to determine erectness of a variety in small clonal plots at one location. The larger outfield plots at 13 locations are better for assessing the relative erectness and harvestability of new varieties. Agronomists working at the outfield level agreed that yield data should be taken on CP 65-357 although these data are not normally taken on discontinued varieties. The outfield data showed that CP 65-357 was the most outstanding variety in yield in the combined analysis of 10 light soil experiments during 1970 (6). Studies of cold tolerance also showed that CP 65-357 had a high degree of mill-cane cold tolerance (8). Furthermore, many of the mosaic-resistant varieties under test were very disappointing in yield or harvestability. After a careful review of these data, the variety advance- ment committee decided to bring CP 65-357 back into the program and transfer it to the secondary increase stations in 1971.
1/ Based on research done cooperatively with M. J. Giamalva, Department of Outfield Sugars, Louisiana Agricultural Experiment Station, Baton Rouge, Louisiana.
1972 OUTFIELD RESULTS
Yield data from outfield tests are normally grouped into light soil and heavy soil. The industry has historically been divided into the Mississippi River-Bayou Lafourche, the Bayou Teche, and the Red River areas. A combined analysis is made for each group by using all experiments from all areas. The best varieties for the La. sugar industry are those that yield best as an average of all locations in the combined analysis. Major varieties occupy large acreages in all areas.
The yields of CP 65-357 were compared with those of commercial varieties in the 3 areas during 1972 (Tables 1 - 3 ) . It was the highest yielding variety in sugar per hectare in the Mississippi River-Bayou Lafourche and Bayou Teche areas. CP 65-357 and L 65-69 were the highest in sugar per hectare in the Red River area. There was relatively little difference in ranking of varieties for the different areas. For example, CP 65-357 was the highest yielding variety and CP 52-68 was the lowest in all 3 areas. There- fore, a single combined analysis of the data for all locations from the 3 areas produced the same interpretation. A combined analysis of all areas is normally used for variety recommendations.
CP 65-357 seems well adapted to the heavier soil types, but yield data on those heavy soil experi- ments are still limited and are not shown here.
CP 65-357 is compared with the Louisiana commercial varieties for the more important variety charac- teristics in Table 4. Two major weaknesses of CP 65-357 are mosaic susceptibility and intolerance to RSD.
It is as susceptible to mosaic as CP 52-68, and very difficult to rogue. CP 65-357 was impossible to rogue at several outfield locations, so we had to use mosaic-infected seed cane to establish the variety in the outfield tests. Limited data suggest that CP 65-357 is tolerant to the disease. The variety must be tolerant if it is to become a major sugarcane variety. CP 65-357 is susceptible and intolerant to RSD and growers are urged to heat treat their seed cane.
Table 4. Comparisons of CP 65-357 with other La. varieties for important characteristics.
Although CP 65-357 is susceptible to the major virus diseases, it rated good to very good for most variety characteristics important in Louisiana such as tonnage, sugar, erectness, cold tolerance, borer resistance, and purity.
A survey of Louisiana sugarcane growers conducted by Hicks (7) after the 1971 harvest season in- dicated the most desirable characteristic in a sugarcane variety would be ease of mechanical harvesting.
CP 65-357 has shown very good erectness at the outfield level in the difficult-harvesting seasons of 1970, 1971, and 1972. CP 65-357 compares favorably with CP 52-68, the high standard for erectness, and should provide the sugar industry with a good harvesting variety.
Although CP 65-357 was selected and released for the Louisiana sugarcane industry, it is also being tested in Florida and south Texas. Preliminary data from these areas indicate it may be adapted to these regions.
REFERENCES
1. Abbott, E. V. 1971. History of the U.S. Sugar Cane Field Station at Houma, La. Sugar Y Azucar 66(10): 69-71.
2. Breaux, R. D. 1971. Selection for erectness in sugarcane in Louisiana. Proc. ISSCT 14: 286-296.
3. 1972. Selecting commercial sugarcane varieties from large seedling and clonal pop- ulations. Proc. ASSCT 2(NS):56-66.
4. Fanguy, H. P., and M. J. Giamalva. 1972. Sugarcane variety testing at the outfield level in Louisiana. Proc. ASSCT 2(NS):71-72.
5. , and R. L. Tippett. 1968. Variety yield trials used to measure rate of mosaic spread in sugarcane. Sugar y Azucar 63(5):56-57.
6. Giamalva, M. J. 1971. Outfield evaluation of sugar cane varieties in 1970. Sugar Bull.
49(24):350-354.
7. Hicks, E. J. 1972. Down the row with Earl Hicks. Sugar Bull. 50(23):6.
8. Irvine, J. E. 1971. Freeze resistance in varieties of mature sugarcane. Sugar Bull. 50(6):9-14.
9. Matherne, R. J. 1968. A history of major Louisiana sugarcane varieties. Proc. ISSCT 13: 1057-1061.
10. 1971. Early testing for higher yielding varieties: USDA infield variety program.
Proc. ASSCT 1(NS):121-123.
BREEDING FOR RESISTANCE TO MOSAIC STRAIN H IN LOUISIANA R. D. Breaux and P. H. Dunckelman Southern Region, Agricultural Research Service
U.S. Department of Agriculture Houma, Louisiana1/
ABSTRACT
A breeding program to combine a high degree of resistance to strain H of sugarcane mosaic with high yield was initiated in 1960. Interspecific hybrids with the highest degrees of resistance were identified and hybridized with high-yielding susceptible varieties, and selection pressure was in- creased in seedling and early clonal progenies. Because of the narrowness of the genetic base of the few resistant interspecific hybrids available (only two original Saccharum spontaneum L. varieties), several hundred S. spontaneum clones were screened for mosaic resistance. One form, US 56-15-8, yielded some clones in the BC2 progeny within the commercial range for most agronomic characteristics, yet highly resistant to mosaic. BC3 and intercross progeny of these clones are presently being screened.
The behavior of these crosses is compared to that of crosses from the old breeding lines. Although it will be necessary to release high-yielding, susceptible but tolerant varieties for the present, these data indicate that resistant high-yielding varieties will again be available in the future.
HISTORY OF MOSAIC
The role that sugarcane mosaic played in the decline of the Louisiana sugarcane industry in the mid-1920's needs no retelling. The disease was an important cause of yield reduction for 25 years, until highly resistant CP varieties replaced the susceptible but tolerant POJ and Co varieties. The breeding of resistant varieties eliminated mosaic as a major disease problem for more than 15 years.
In 1956, Abbott (1) noticed an unusual amount of mosaic spread in commercial fields of NCo 310 and CP 44-101 in Lafourche and St. Charles Parishes. The rapid spread of mosaic in the susceptible NCo 310 was surprising, and infections as high as 28% in plant-cane fields of the supposedly resistant CP 44-101 were totally unexpected. Abbott correctly surmised that Louisiana had a new strain of sugarcane mosaic virus (SCMV). He later described it as strain H (3).
Although he did not immediately predict the extent to which the new strain of mosaic would spread, Abbott noted that it could infect the major commercial variety CP 44-101. NCo 310, which was then being increased, was highly susceptible, and the newly released CP 52-68 was also susceptible — all of which pointed to the possible danger of another mosaic epidemic. Abbott recommended to growers that they resume rogueing their fields. He initiated studies into the susceptibility and tolerance to the new strain of the major commercial varieties, promising unreleased varieties and potential parent varieties.
In 1959, Abbott (2) reported that, of the most promising commercial varieties, CP 52-68 was the least tolerant to mosaic, CP 44-101 was intermediate but also relatively tolerant, and NCo 310 was tolerant and least affected by Mosaic. He also noted that of the 8 varieties recommended for commercial production in 1959, only 3 — CP 36-13, CP 47-193, and CP 44-155 showed a high degree of resistance to mosaic. The resistant varieties produced less sugar per acre than CP 44-101, CP 52-68, or NCo 310, were generally less adapted, and had other undesirable agronomic characteristics that limited their use- fulness as commercial varieties. Although Abbott warned that mosaic spread in NCo 310 was so rapid it was impossible to control the disease in this and other susceptible varieties grown near it, he pointed out that NCo 310 was tolerant and would give satisfactory and perhaps higher yields than the resistant varieties that would have to be substituted for it.
Since there were no high-yielding commercial varieties resistant to strain H, it was necessary for the Louisiana sugar industry to rely on mosaic-susceptible varieties throughout the 1960's and to the present. Strain H spread rapidly throughout the sugarcane belt, and, except in the northern area and a few properties elsewhere, the disease can no longer be controlled in Louisiana's commercial sugarcane
Fortunately, the interspecific hybrids, particularly NCo 310, were tolerant to strain H. Further- more, the active breeding programs of the USDA and the Louisiana Agricultural Experiment Station provided
1/ Research at this location is done in cooperation with the Louisiana Agricultural Experiment Station.
the industry with new susceptible varieties, but either mosaic-tolerant or high-yielding, almost as fast as older varieties succumbed to infection. L 60-25, though intolerant, was released relatively free of mosaic, and was available for partial replacement of CP 52-68 acreage that became saturated with mosaic.
The more tolerant L 62-96 and moderately resistant CP 61-37 are presently replacing much acreage of the saturated non-tolerant L 60-25. Presumably, if it is tolerant, CP 65-357, to be released in 1973, will hasten this replacement of CP 52-68 and L 60-25. This has played a major part in minimizing the harmful effects of the disease.
Major yield reductions from mosaic have thus far been avoided. In fact, sugar-per-acre yields in- creased steadily in Louisiana in the 1960's in spite of this worsening mosaic situation (8).
However, the forced reliance on mosaic-susceptible varieties in this latest epidemic was not without its disadvantages and financial losses to the Louisiana sugar industry. Growers had to return to rogueing seed plots, particularly of susceptible, intolerant varieties. Not only was rogueing costly, but more often than not, mosaic could not be controlled in these susceptible varieties. Replacement of susceptible, intolerant varieties was not complete; in fact more than half of the 1973 crop was planted to CP 52-68 and L 60-25. Much of the acreage of these varieties is saturated with mosaic. The industry could conceivably lose millions of dollars from mosaic in CP 52-68 and L 60-25 in 1973 alone. Yields increased during the 1960's in spite of mosaic. Actually, mosaic strain H robbed the Louisiana sugar industry of gains it made in variety improvement, better borer control, better weed control, improved drainage, and better farming.
A tremendous pool of mosaic inoculum was built up in the 1960's in all but the Northern area of the Louisiana sugarcane belt. Field spread is so intense that rogueing, although still recommended, is of little practical value for mosaic control on a commercial scale in many areas. The increased rate of mosaic spread in susceptible and even moderately resistant varieties is alarming. CP 52-68, released in 1958, was kept below the mosaic saturation point for almost 10 years after its release. L 60-25, re- leased in 1966, has been saturated with mosaic for several years. L 62-96, released in 1969, is already almost 100% mosaic-infected in the Western area of the belt. There is little mosaic-free seed of CP 65-357 for release to sugarcane growers in the fall of 1973. Field spread of mosaic is now so intense it is extremely doubtful that the industry can use a mosaic-susceptible variety that is not tolerant to strain H of sugarcane mosaic.
The mosaic virus has shown a surprising stability in this tremendous pool of inoculum. Only one other strain (strain I) has been positively identified in Louisiana since 1958 (9). Although it is significantly more damaging to current commercial varieties than strain H, it has not spread as rapidly as the latter strain (10).
Everyone in the Louisiana sugarcane industry recognizes that the use of mosaic-tolerant varieties was a necessary stopgap measure; varieties with high mosaic resistance and equally high yielding ability would be greatly preferred. Commercial varieties have changed since Abbott described the mosaic strain H-variety complex in 1959 (2). However, the situation today is very much like the one he described 14 years ago. L 62-96 and CP 65-357, infected with mosaic, will produce satisfactory and perhaps higher yields than the more resistant varieties that can be substituted for them, namely, CP 48-103, CP 61-37, and L 65-69. Consequently, growers must still rely on susceptible, tolerant varieties.
Abbott and Zummo (4) predicted that breeding high-yielding mosaic-resistant varieties would be even more difficult than in the past, because of the scarcity of resistant germplasm among promising interspecific hybrids and because of the susceptibility of the S, spontaneum clones (5) that formed the genetic base for mosaic resistance in Louisiana sugarcane varieties. This has certainly been the case;
however, measurable progress has been made in identifying new sources of resistance to SCMV strain H and in broadening the genetic base for resistance. It is the purpose of this paper to summarize these efforts.
VARIETY RESISTANCE TO STRAIN H Resistant Interspecific Hybrids.
Abbott and Zummo (5) found that only 9 of 337 potential parent varieties remained completely free of mosaic at Waterford Plantation in the Mississippi River area between 1960-1962. Most of the resistant varieties were not considered high-quality parents from an agronomic standpoint, and some were abandoned on the basis of their poor performance in crosses. Only 3 of these resistant varieties, CP 33-229, CP 36-13, and CP 50-40, were subsequently used as parent clones (Table 1 ) . Continued field-exposure trials by agronomists and pathologists have since identified 11 additional resistant interspecific hybrids suitable as parent canes. They were introduced into the crossing program as soon as they were identified. One of these varieties, L 65-69, was released to the industry in 1972.
Fig. 1. Parentage of the CP 1971 varieties used as new sources of mosaic resistance at Houma and Canal Point in 1973.
Table 1. CP and L varieties with resistance to mosaic strain H in the field and greenhouse which have been used as parents since 1962.
Abbott and Zummo (5) also identified some moderately resistant interspecific hybrids that took but little mosaic at Waterford. Some of these were better agronomically than the more resistant varieties and were already being widely used as parents in the commercial breeding program. The list of moderate- ly resistant varieties has also been substantially lengthened since 1962 (Table 1 ) . One of these moderately resistant varieties, CP 61-37, was released to the industry in 1969. Moderately resistant varieties like CP 61-37 would require little rogueing and remain relatively mosaic-free in light or moderate spread areas. However, they take considerable mosaic in heavy spread areas, and a careful rogueing program would have to be followed to control mosaic in these varieties.
Resistance from New S. spontaneum lines.
More than 260 clones of S. spontaneum were artifically inoculated and screened for resistance to sugarcane mosaic from 1964-1968 at the Houma station (7). Thirty-two apparently immune S. spontaneum clones were studied in detail, and 10 new breeding lines for mosaic resistance are in various stages of backcrossing and selection.
US 56-15-8, a S. spontaneum from northern Thailand, was one of the highest sucrose S. spontaneum clones of the 32 clones studied. Records showed that US 56-15-8 was crossed by C. 0. Grassl to CP 52-1 in 1959 and backcrossed to CP 57-101 and C1 54-134 in 1961 (Fig. 1 ) . Two of the BC1 progeny (CP 63-561 and CP 63-571) were selected at Houma in 1963 and returned to Canal Point. We requested and received B C2 progenies of US 56-15-8 at Houma in 1967.
The BC2 progenies were surprisingly promising agronomically and yielded varieties of apparent com- mercial caliber. Eight of these varieties are being tested as commercial possibilities. In 1972-73, breeders used 10 of these BC2 clones (1971 CP varieties) extensively in crosses (Table 2 ) . None of the 10 varieties had ever taken mosaic in severe greenhouse-inoculation tests; however, CP 71-400, CP 71-405, and CP 71-421 recently took significantly more mosaic than L 65-69 in a preliminary field-ex- posure test (data not shown).
Table 2. Number of seedlings transplanted to field from BC2 progeny of a new source of mosaic resistance, US 56-15-8 (S. spontaneum), in 1973.
Mosaic resistance can still be found in the B C2 progenies that were tested in the greenhouse this spring. The average percentage of healthy seedlings in BC3 progenies and intercross progenies from US 56-15-8 crosses was higher than in progenies from the old breeding lines (Table 3 ) . Mosaic in- fection was recorded in 300 seedlings of each progeny 30 days after inoculation with a mixture of strains 11 and 1 extracted from Rio sorghum at 1:10 dilution.
Table 3. The average percentage of healthy seedlings in progenies from old resistance sources and from US 56-15-8 (S. spontaneum) crosses after inoculation with mosaic in the greenhouse.
Only 10.1% of the seedlings that came from 9 crosses from susceptible x moderately resistant inter- specific hybrids of old breeding lines remained free of mosaic after inoculation. The frequency of healthly seedlings was also low (1.4.3%) in 4 L 65-69 (susceptible x resistant) progenies. Twice as many seedlings remained healthy when the 1971 CP varieties from US 56-15-8 were crossed to susceptible CP and L varieties. Forty-one percent of the seedlings remained free in 11 progenies derived from crosses be- tween the US 56-15-8 derivatives and moderately resistant CP and L varieties. More than half of the seedlings (57.2%) remained free of mosaic in the intercross progenies between the 1971 CP varieties from US 56-15-8.
RESISTANT GERMPLASM AND INCREASING SELECTION PRESSURE
The gradual accumulation of more and better sources of mosaic resistance has made it possible to test a greater number of seedlings from mosaic-resistant parents (Table 4 ) . Fewer than 3,500 seedlings were transplanted to the field each year from mosaic-resistant parents in the period 1960-1962. Between 1970 and 1972, however, more than 45,000 of about 75,000 seedlings grown each year at Houma had at least one mosaic-resistant parent. All crosses, except those made for special purposes such as cold-tolerance or borer resistance, have at least a moderately resistant parent.