Barry Glaz

Orange Rust Effects on Leaf Photosynthesis and Related Characters of Sugarcane

Orange rust of sugarcane (Saccharum spp. hybrids), caused by Puccinia kuehnii, is a relatively new disease in the Western Hemisphere that substantially reduces yields in susceptible sugarcane genotypes. The objective of this study was to determine the physiological mechanisms of orange rust-induced reductions in sugarcane growth and yield by quantifying effects of the disease on leaf SPAD index (an indication of leaf chlorophyll content), net photosynthetic rate, dark respiration, maximum quantum yield of CO2 assimilation, carbon fixation efficiency, and the relationships between these leaf photosynthetic components and rust disease ratings. Plants growing in pots were inoculated with the orange rust pathogen using a leaf whorl inoculation method. A disease rating was assigned using a scale from 0 to 4 with intervals of 0.5. At disease ratings ≥2, the rust-infected leaf portion of inoculated plants showed significant reductions in SPAD index, maximum quantum yield, carbon fixation efficiency, stomatal conductance, leaf transpiration rate, and net photosynthetic rate; but the rusted portion of the infected leaves had increased intercellular CO2 concentration and leaf dark respiration rate. Although leaf SPAD index, photosynthetic rate, stomatal conductance, and transpiration rate at the rust-infected portion decreased linearly with increased rust rating, the effect of orange rust on photosynthetic rate was much greater than that on stomatal conductance and transpiration. Unlike earlier reports on other crops, reduction in leaf photosynthesis by orange rust under low light was greater than that under high light conditions. These results help improve the understanding of orange rust etiology and physiological bases of sugarcane yield loss caused by orange rust.

Promoting Utilization of Saccharum spp. Genetic Resources through Genetic Diversity Analysis and Core Collection Construction

Sugarcane (Saccharum spp.) and other members of Saccharum spp. are attractive biofuel feedstocks. One of the two World Collections of Sugarcane and Related Grasses (WCSRG) is in Miami, FL. This WCSRG has 1002 accessions, presumably with valuable alleles for biomass, other important agronomic traits, and stress resistance. However, the WCSRG has not been fully exploited by breeders due to its lack of characterization and unmanageable population. In order to optimize the use of this genetic resource, we aim to 1) genotypically evaluate all the 1002 accessions to understand its genetic diversity and population structure and 2) form a core collection, which captures most of the genetic diversity in the WCSRG. We screened 36 microsatellite markers on 1002 genotypes and recorded 209 alleles. Genetic diversity of the WCSRG ranged from 0 to 0.5 with an average of 0.304. The population structure analysis and principal coordinate analysis revealed three clusters with all S. spontaneum in one cluster, S. officinarum and S. hybrids in the second cluster and mostly non-Saccharum spp. in the third cluster. A core collection of 300 accessions was identified which captured the maximum genetic diversity of the entire WCSRG which can be further exploited for sugarcane and energy cane breeding. Sugarcane and energy cane breeders can effectively utilize this core collection for cultivar improvement. Further, the core collection can provide resources for forming an association panel to evaluate the traits of agronomic and commercial importance.

Vigor Rating and Brix for First Clonal Selection Stage of the Canal Point Sugarcane Cultivar Development Program

A better understanding of sugarcane (Saccharum spp.) genetic variability in agronomic performance will help optimize breeding and selection strategies. Vigor ratings and Brix data were collected from the 2009 and 2010 clones in the first clonal selection stage (stage I) of the Canal Point (CP) sugarcane cultivar development program. Stage I individual selection was based on disease resistance and on the product of vigor and Brix. Vigor ratings (from 1 to 9) from all clones and Brix of any clones with a vigor rating ≥6 were collected in the stage I fields and analyzed for relationships between vigor and Brix, for selection rate in each family (i.e., cross), and for their coefficients of variation (CV) within and among families. There was no correlation between vigor and Brix, suggesting that it would be feasible in stage I to select sugarcane clones with both high vigor and high Brix. Variability was high (CV = 59%) for both the number of planted clones and selection rates among families, and vigor (7.2%) had greater CV than Brix (5.4%). Averaged across years, the within-family CVs (9.3% for vigor and 6.3% for Brix) were greater than the among-family CVs (6.3% for vigor and 4.7% for Brix). Results indicated that greater emphasis on family-based than on individual selection in stage I should be avoided, as it would result in the loss of potentially productive clones. However, use of individual selection data on vigor and Brix for analyzing family performance should improve parental selection and optimize crosses.

Field Response of Sugarcane Genotypes to Freeze Stress with Genotype x Environment Effects on Quality Traits

Freeze stress negatively affects sucrose yield in sugarcane (Saccharum spp. hybrids), particularly during the harvest season. To understand its impact on the performance of genotypes in the Canal Point (CP) breeding program, the genotype-environment (GxE) interaction was appraised via additive main effects and multiplicative interactions (AMMI) analysis and group-based trajectory modeling (GTM). Forty-five selections of the CP01, CP02, and CP03 series and three cultivars were examined in replicated field tests at Hague and Canal Point, Florida, in the plant-cane (CP01-CP02 in 2006-07) or through the first ratoon (CP03 in 2007-09). Profile analyses of Brix, pol, and sucrose content (SC) were developed from stalks sampled at different times of year to follow their deterioration. Hague experienced more intense freeze nights (17–22 d yr−1 with temperatures [TC] from −0.4 °C to −8 °C) than CP (2 nights, rarely down to −2 °C). Temperatures ≥−2 °C increased SC in a majority of the genotypes and TC ≤ −4 °C hastened juice deterioration. The response was nonlinear when TC gradually declined from 0 ° to −4 °C, but linear after early freeze of ≤−4 °C. The AMMI analysis was appropriate for interpreting the GxE interaction variation, indicating a greater contribution from environments (location-year-sampling combinations) than from G or GxE interaction. The AMMI and GTM identified two to four reaction norms as differential performance under freeze: a susceptible group in the minority with SC declining constantly with TC; the other groups typifying the common profile had an increase in SC with TC ≥ −2 °C and a decline with TC ≤ −4 °C. Genotypes with the highest SC at the onset of freeze tended to hold this level longer than those with the lowest content. The identification of different reaction norms suggests that a genetic component may underpin freeze adaptation in modern sugarcane cultivars relative to the old tropical hybrids. However, breeding efforts to increase the tolerance of sugarcane cultivars to temperatures <−3 °C must be given due consideration.

Repeatability between two intermediate sugarcane genotype selection stages in Florida.

Improved yield and disease resistance on sand soils are priorities of the Canal Point (CP) sugarcane (Saccharum spp.) breeding and selection program. Analyses of historical phenotypic data can provide helpful information in guiding selection strategies to meet these priorities. Correlation analysis was used to examine repeatability of phenotypic data used to advance genotypes from an unreplicated single location clonal crop test (stage II) to the subsequent stage (stage III; two replicate, four location clonal crop experiment). Correlations between data for four traits measured in stage II and the corresponding data pooled across soil types for the same genotypes in stage III varied across 23 series of the CP program. Generally, when correlations were statistically significant (P < 0.05), correlation values were low (means; theoretical recoverable sucrose (TRS) r = 0.40, cane yield r = 0.27, and economic index r = 0.23). Similar trends were evident for correlations between data from stage II and stage III on muck soil and stage II and stage III on sand soil across 10 series of the CP program. A 10% reduction in the number of genotypes advanced to stage III over that period would have meant losing only 1 and 13 genotypes that had commercial potential on muck and sand soils, respectively (n = 1278). Correlations between the phenotypic data were significant only for stage III comparisons between TRS and cane yield, which were negatively associated on either soil type. These results indicate that changes in the advancement strategy from stage II are not required as advancing approximately 135 genotypes identifies almost all genotypes with the genetic potential to yield well on muck or sand soils in stage III. Increasing genotypes in stages prior to stage III and changing crossing strategies to improve identification of disease-resistant, high-yielding genotypes for sand soils is recommended.

Sugarcane Response to High Water Tables and Intermittent Flooding

Sugarcane production has engendered environmental concerns of nutrient transfer and subsidence of organic soils. Retaining water on fields would ameliorate these environmental issues. The objective of this research was to document the growth of sugarcane subjected to various high water-table treatments. Two experiments were conducted across two years using three sugarcane cultivars grown outdoors in large pots. Key aspects were to examine the timing of when water-table treatments were imposed and the influence of intermittent flooding. Continuous flooding at all growth stages was deleterious. A continuous water table at a 15 cm depth below the soil surface resulted in no negative effect on cane yield. Intermittent flooding in cycles of 6 d flooding, followed by 15 d at either a 15 cm or 45 cm water table, did not decrease yields. These results indicated that there may be practical management options for sustaining sugarcane production at high water tables.

Sugarcane Response to Month and Duration of Preharvest Flood

Abstract Extending duration of moderately used 1-day preharvest floods in sugarcane (Saccharum spp.) could improve Florida sugarcane insect control, freeze protection, and soil conservation, and reduce unwanted P discharge. The purpose of this study was to compare the effects of flood duration and month of flood application on theoretical recoverable sucrose (TRS), cane yield, and sucrose yield of four sugarcane cultivars. During the plant-cane and first-ratoon crop cycles, 0-, 10-, or 20-day floods were applied in November or to lysimeters planted with cultivars CP 72-2086, CP 80-1827, CP 89-2143, and CP 92-1666. Cane and sucrose yields of flooded treatments were at least as much as those of non-flooded controls. These results warrant research to quantify the profitability of preharvest flooding of sugarcane, recognizing that these 10-20 day floods had minimal impact on yields while offering potential economic returns from other agronomic and ecologic benefits.

Historical Use of Cultivars as Parents in Florida and Louisiana Sugarcane Breeding Programs.

Sugarcane (Saccharum L. spp. hybrids) growers depend on breeding programs for new, high-yielding cultivars that have resistance to abiotic and biotic stresses, so breeders continually seek out widely adapted, high yielding germplasm to be used as parents for their programs. Cultivars are sometimes used for this purpose, but their use may be minimized to prevent genetic diversity erosion. The purpose of this study was to determine the importance of cultivars as parents in three USA (one in Florida and two in Louisiana) sugarcane breeding programs by quantifying the percentage of cultivars that had these parental groupings based on published registrations and crossing records. The percentage of cultivars with at least one commercial parent for each program was 81.8%, 77.5%, and 64.3% for the Houma (Ho), Louisiana, Canal Point (CP), Florida and Louisiana State University (LSU) programs, respectively, but cultivars were recently used as parents in only 11.8% (Ho), 16.39% (CP), and 34.3% (LSU) of crosses. The results indicate that the CP and Ho programs should consider increasing the use of cultivars as parents in their breeding programs to increase the probability of selecting potential commercial genotypes, but this should be balanced with high diversity crosses to avoid the loss of diversity.

Character association and selection indices in sugarcane.

Sugarcane is an important crop of Khyber Pakhtunkhwa province of Pakistan. However, the yield per unit area is below some advanced sugarcane growing areas of the world, and the national average of Pakistan. Improved methods of selection resulting in higher yielding sugarcane cultivars would help in increased yield. Information about direct and indirect effects of yield contributing characters and subsequently developing a selection index would greatly improve the process of cultivar development. An experiment comprising 26 sugarcane genotypes coupled with 2 check cultivars was grown in a randomized complete block design with 3 replications at Sugar Crops Research Institute, Mardan, Pakistan during 2011-2013. Data were collected on stalk and yield attributes. Genotypic path coefficients revealed that Tiller2, growth2, and Pol had positive direct effects on cane yield. Selection indices based on growth2, Pol, tiller2, and cane yield showed that individuals selected based on these characters simultaneously gave a genetic advance of above 60. CPF-225, MS-2003-CR5-245, MS-2003-CR7-243, and MS-2003-CR8-407 could be selected as the best genotypes according to these selection indices. This study showed that applying path coefficient analyses followed by development of selection index could be a worthwhile selection strategy.

Leaf Phosphorus Diagnosis of Sugarcane on Organic Soils

ABSTRACT Most of the sugarcane (interspecific hybrids of Saccharum sp.) production in Florida is on organic soils. Supplemental phosphorus (P) fertilizer is often applied for optimum yields, but producers are required to reduce P levels in farm drainage waters. The objectives of this study were to relate optimum leaf P tissue concentration with yield in organic soil, and to determine optimum leaf sampling dates during the summer. Eight genotypes were planted at two locations, eight additional genotypes were planted at a third location, and eight more genotypes were planted at a fourth location. Crops were grown for three years. Measurements of leaf P concentration were repeated during growth seasons and over crop years for a total of six sampling dates at each location. Three fertilizer P treatments (0, 24, and 48 kg ha−1 yr−1) were applied to all genotypes at each location. Leaf samples were partitioned into early-, mid-, and late-summer dates. Early-leaf samples had the widest range in leaf P concentrations compared with mid- and late-season leaf samples. Correlation analyses of yield vs. leaf P concentration across all treatments in early- and mid-summer were statistically significant (P < 0.05), but coefficients were low (r = 0.14 and 0.26, respectively). No consistent relationship across locations described the effect of leaf P tissue concentration on yield. Leaf P concentrations could not provide accurate P fertilization rates that will give maximum sugarcane yields and prevent over-fertilization of P. The highest potential for relating leaf P concentrations with yield appears to be from early leaf samples.