Saccharum Hybrid Research Articles

Influence of drought stress on Mexican rice borer (Lepidoptera: Crambidae) oviposition preference in sugarcane

Two sugarcane, Saccharum hybrids, varieties were grown in the greenhouse under well watered or drought conditions to examine the influences of stress on Mexican rice borer, Eoreuma loftini (Dyar), oviposition preference and selected nutritional components without impinging factors common to field conditions that alter responses. Our research revealed that, under controlled conditions, drought induced a wider range and greater uniformity of free amino acid (FAA) accumulations than have been previously reported. Drought stress resulted in increased dry leaf tissue and elevated concentrations of 7 of 9 detectable free essential (for insect health) amino acids in stalks, the chief food of Mexican rice borer larvae. Stressed sugarcane was preferred for oviposition, likely related to greater numbers of dry leaves and heightened host plant nutritional quality. Dry leaf tissue, which is not consumed, may be a cue for improving chances of larvae encountering nutrient-enhanced living tissue, and for concealing eggs in folds. Excised dry leaf tissue from the treatments was indistinguishable for oviposition preference; therefore, biochemical status of living tissue may provide oviposition cues. Varieties exhibited no major genotypic differences in FAA accumulations or oviposition preference.

Sugarcane Postharvest Residue Management in a Temperate Climate

Full retention of sugarcane (interspecific hybrids of Saccharum spp.) postharvest residue may reduce ratoon crop yields. The objective of this study was to determine the effects of different residue removal timings and methods on sugarcane yield. A two‐factor (timing and method) experiment was conducted on both clay and silt loam soils in southeastern Louisiana. Removal timings consisted of the following physiological stages: predormancy, complete dormancy, intermediate dormancy, and postdormancy. Removal methods consisted of partial removal from the row top by mechanical means, complete removal by burning, and no removal (control) applied to first, second, and third ratoons. Sugar yields following burning at predormancy (6800 kg ha−1), complete dormancy (6610 kg ha−1), and mechanical removal at predormancy (6500 kg ha−1) were greater than the control (6190 kg ha−1) for all ratoons. Burning at postdormancy decreased sugar yields by 440 kg ha−1 relative to the control. Ratoons responded similarly to the residue management practices evaluated, and effects were consistent on both clay and silt loam soils. Results show that the residue generated during the green‐cane harvesting of sugarcane in Louisiana should be removed from harvested fields as soon after harvest as possible to ensure optimum yields of subsequent ratoon crops.

Changes in an Inceptisol of Mauritius after rock removal for sugar cane production

Sugar cane ( Saccharum hybrid sp.) cropping in the rocky soils of Mauritius requires the prior removal of rocks to enable the implementation of mechanized operations, particularly harvesting. The effects of such operations on the soil are unknown, particularly the extent to which soil properties could be affected. A study was conducted at a sugar estate on the sub-humid western coast of Mauritius to determine whether the properties of an Inceptisol had been degraded on account of rock removal and land preparation. Pristine uncultivated soils were compared to sugar cane soils from which rocks had been removed, either recently, i.e. about 2 years ago, or earlier, i.e. about 10 years ago. A number of biological, chemical and physical properties were studied. These comprised organic matter and microbial biomass; pH, cation exchange capacity and exchangeable bases; particle size distribution, aggregate stability, bulk density, plant available water and infiltration rate. The results indicate that biological properties have degraded in the topsoil but improved in the subsoil, chemical properties have generally improved, whereas physical properties were both positively and negatively affected. Thus, organic carbon concentration decreased from about 3.9% to 3.2% in the 0–5 cm layer following rock removal, but increased from about 1.8% to 2.3% in the 15–30 cm layer. Soil pH increased significantly, from 6.9 to 7.5 in the topsoil and from 7.0 to 7.7 in the subsoil. The concentration of exchangeable bases also tended to increase. Stabilized water infiltration rate increased from 133 to 185 mm/h and plant available water increased from 42 to 58 mm. However, bulk density also increased from 0.96 to 1.02 g/cm 3 in the 0–5 cm layer and from 1.09 to 1.23 g/cm 3 in the 15–30 cm layer. While rock removal can explain some of these changes, it is also quite likely that other practices linked to sugar cane production, such as tillage, irrigation and the addition of organic waste material, played a decisive role in this respect. The greatest cause for concern stemmed from soil compaction. Remedial action that was identified to address the issues of declining topsoil organic matter content included trash blanketing, addition of organic wastes and green manuring, whereas soil compaction could be managed through the use of controlled traffic and minimum tillage and in situ rock crushing.

Sucrose transporter1 functions in phloem loading in maize leaves

In most plants, sucrose is exported from source leaves to carbon-importing sink tissues to sustain their growth and metabolism. Apoplastic phloem-loading species require sucrose transporters (SUTs) to transport sucrose into the phloem. In many dicot plants, genetic and biochemical evidence has established that SUT1-type proteins function in phloem loading. However, the role of SUT1 in phloem loading in monocot plants is not clear since the rice (Oryza sativa) and sugarcane (Saccharum hybrid) SUT1 orthologues do not appear to function in phloem loading of sucrose. A SUT1 gene was previously cloned from maize (Zea mays) and shown to have expression and biochemical activity consistent with a hypothesized role in phloem loading. To determine the biological function of SUT1 in maize, a sut1 mutant was isolated and characterized. sut1 mutant plants hyperaccumulate carbohydrates in mature leaves and display leaf chlorosis with premature senescence. In addition, sut1 mutants have greatly reduced stature, altered biomass partitioning, delayed flowering, and stunted tassel development. Cold-girdling wild-type leaves to block phloem transport phenocopied the sut1 mutants, supporting a role for maize SUT1 in sucrose export. Furthermore, application of 14C-sucrose to abraded sut1 mutant and wild-type leaves showed that sucrose export was greatly diminished in sut1 mutants compared with wild type. Collectively, these data demonstrate that SUT1 is crucial for efficient phloem loading of sucrose in maize leaves.

Effects of sugar cane (Saccharum hybrid sp.) cropping on soil acidity and exchangeable base status in Mauritius

Continuous sugar cane cropping commonly leads to soil acidification. Such an effect can be attributed to N fertilization and to leaching and removal of exchangeable bases. A study was conducted on the five zonal soils of Mauritius to ascertain whether continuous sugar cane cropping was causing the soil pH and level of exchangeable bases to decline to such an extent that it would threaten the sustainability of the island’s sugar industry. Soil pH, K, Ca and Mg concentration were determined for samples that had either been under native vegetation or cropped with sugar cane. Cropping was beneficial to pH in the sub-humid Low Humic Latosol (L) and Latosolic Reddish Prairie (P) and humid Humic Latosol (H) soils, but detrimental in the super-humid Humic Ferruginous Latosol (F) soil. The increased pH in the first three soils was caused by the regular application of pH-enhancing amendments such as lime, coral sand, filter mud and poultry litter. In the F soil, the acidification of the topsoil was accompanied by a pH increase in the subsoil, indicating that bases had been leached down the profile by rainfall. Cropping was not detrimental to exchangeable base status, indicating that current applications of K, Ca and Mg-containing compounds to the sugar cane crop were also generally adequate to compensate for the removal and losses of these elements. Since sugar cane cropping does not lower soil pH or reduce levels of exchangeable bases, it can be concluded that current recommendations with respect to liming and exchangeable base application are adequate for the long-term sustainability of the sugar industry and should be adhered to.

Soil compaction under sugar cane (Saccharum hybrid sp.) cropping and mechanization in Mauritius

Farm machinery is increasingly used in sugar cane production in Mauritius and is expected to cause soil compaction. A study was undertaken to ascertain whether the five major cane-growing soil groups of Mauritius were being compacted as a result of sugar cane cropping and mechanized harvesting. Bulk density was measured in situ using the excavation method and stabilized infiltration rate was determined with the CSIRO disc per-meameter on pristine soils under native vegetation, manually harvested sugar cane soils and mechanically harvested sugar cane soils. Bulk density results were generally not significantly different between pristine soils and manually harvested soils or between manually harvested soils and mechanically harvested soils. The only exception was in the super-humid Latosolic Brown Forest soil, where bulk density was significantly higher in the manually harvested soil by up to 0.4 g cm- 3 compared to the pristine soil. The stabilized infiltration rate of the sub-humid Low Humic Latosol and Latosolic Reddish Prairie soils was significantly higher with manually harvested sugar cane under irrigated conditions compared to pristine conditions, increasing from about 100 mm h- 1 to more than 200 mm h- 1. The mechanically harvested soils had significantly lower stabilized infiltration rate than the manually harvested soils, a minimum value of 55 mm h- 1 being measured in the Humic Latosol. It appears that compaction is not serious enough to affect sugar cane yield, as the bulk density of the soils under sugar cane in Mauritius varies between 1.0 and 1.3 g cm- 3, still lower than the threshold values of 1.5 to 1.7 g cm- 3 that were determined for other countries. However, the threshold values applicable for Mauritius must be determined before any firm conclusion can be drawn. There is a greater risk of runoff and erosion under high intensity rainfall with mechanized harvesting, and management of sugar cane plantations should aim at reducing or alleviating topsoil compaction. It is therefore suggested that minimum tillage and controlled traffic are the two most appropriate strategies for reducing compaction in the sugar industry of Mauritius.

Dry matter partitioning and quality of Miscanthus, Panicum, and Saccharum genotypes in Arkansas, USA

The partitioning and quality of aboveground biomass have important ramifications for crop management and biomass conversion. In preliminary studies, Saccharum sp. � Miscanthus sp. hybrids exhibited stubble cold tolerance in west-central Arkansas, unlike Saccharum sp. � Saccharum spontaneum hybrids. The objective was to examine foliar and stem quality of the C4 grasses Miscanthus sinensis (‘Gracillimus’), Miscanthus x giganteus (Q42641, proprietary), Panicum virgatum (‘Alamo’), and two F1 hybrids of Saccharum sp. � Miscanthus sp. (US84-1028 and US84-1058) in a field study during 2004 (plant cane) and 2005 (first

Influence of Nonoptimal Ripener Applications and Postharvest Residue Retention on Sugarcane Second Ratoon Yields

Retention of sugarcane (interspecific hybrids of Saccharum spp.) postharvest residue and certain glyphosate ripener application regimes may independently reduce yields of the subsequent ratoon crop in wet climates. The objective of this experiment was to determine the effects of ripener application and ripener treatment to harvest intervals (THI) on yields of the treated first ratoon, and the combined effects of these treatments and postharvest residue retention on the subsequent second ratoon. Whole plots consisted of either a nontreated control or 0.21 kg a.e. ha−1 glyphosate applied to the first ratoon of cultivar LCP 85–384. Split‐plots consisted of THI of 40, 50, and 60 d for all plots. Split‐split plot treatments consisted of partial removal of postharvest residue or complete retention for second ratoon. Averaged across all THIs for the first ratoon, glyphosate increased sucrose yield by 300 kg ha−1 compared with the control. The 60 d THI reduced second ratoon cane and sucrose yields by 5.4 Mg ha−1 and 900 kg ha−1, respectively, compared with the means of the 40 and 50 THI and sucrose yields by 300 kg ha−1 compared with the control. Full residue retention reduced second ratoon cane and sucrose yield by 2.3 Mg ha−1 and 300 kg ha−1, respectively, compared with partial removal. Residue retention and glyphosate application were not negatively synergistic. Producers should remove postharvest residue from the row top and harvest ripener‐treated cane at a THI of 40 to 50 d to maximize sucrose yields in the first ratoon while also preventing yield losses in the subsequent second ratoon.

Soil organic matter and microbial biomass as influenced by sugar cane (Saccharum hybrid sp.) production practices in Mauritius

Sugar cane has been grown in Mauritius for over 350 years in a monocropping system. As a result, soil quality could have declined since productivity has been stagnating over the last twenty years in spite of improved agronomic practices and higher-yielding varieties. A study was therefore initiated to determine the effects of sugar cane production practices on the biological quality of the major soil groups of Mauritius. Organic matter (OM) and microbial biomass contents were determined for soils with different cropping histories, namely native vegetation, cropping with sugar cane under manual conditions, and cropping with sugar cane under mechanized conditions. When virgin soil was compared to manually-cropped soil, OM content was found to decrease with cropping in the topsoil, but to increase in the subsoil as a result of soil mixing through tillage. Microbial biomass also decreased in the topsoil as the microbial population had less OM to feed on. When manually-cropped soil was compared to mechanically-cropped soil, both OM and microbial biomass tended to decrease with mechanization as the soil was highly disrupted following land preparation. This decline in soil biological quality will continue if remedial measures are not taken, the latter being trash blanketing, addition of substantial amounts of organic wastes, and the incorporation of leguminous green manures within the cropping cycle, among others.

Relationship Between Sugarcane Rust Severity and Soil Properties In Louisiana

ABSTRACT The extent of spatial and temporal variability of sugarcane rust (Puccinia melanocephala) infestation was related to variation in soil properties in five commercial fields of sugarcane (interspecific hybrids of Saccharum spp., cv. LCP 85-384) in southern Louisiana. Sugarcane fields were grid-soil sampled at several intensities and rust ratings were collected at each point over 6 to 7 weeks. Soil properties exhibited significant variability (coefficients of variation = 9 to 70.1%) and were spatially correlated in 39 of 40 cases with a range of spatial correlation varying from 39 to 201 m. Rust ratings were spatially correlated in 32 of 33 cases, with a range varying from 29 to 241 m. Rust ratings were correlated with several soil properties, most notably soil phosphorus (r = 0.40 to 0.81) and soil sulfur (r = 0.36 to 0.68). Multiple linear regression analysis resulted in coefficients of determination that ranged from 0.22 to 0.73, and discriminant analysis further improved the overall predictive ability of rust models. Finally, contour plots of soil properties and rust levels clearly suggested a link between these two parameters. These combined data suggest that sugarcane growers that apply fertilizer in excess of plant requirements will increase the incidence and severity of rust infestations in their fields.

Growth and metabolism in sugarcane are altered by the creation of a new hexose‐phosphate sink

An efficient in planta sugarcane-based production system may be realized by coupling the synthesis of alternative products to the metabolic intermediates of sucrose metabolism, thus taking advantage of the sucrose-producing capability of the plant. This was evaluated by synthesizing sorbitol in sugarcane (Saccharum hybrids) using the Malus domestica sorbitol-6-phosphate dehydrogenase gene (mds6pdh). Mature transgenic sugarcane plants were compared with untransformed sugarcane variety Q117 by evaluation of the growth, metabolite levels and extractable activity of relevant enzymes. The average amounts of sorbitol detected in the most productive line were 120 mg/g dry weight (equivalent to 61% of the soluble sugars) in the leaf lamina and 10 mg/g dry weight in the stalk pith. The levels of enzymes involved in sucrose synthesis and cleavage were elevated in the leaves of plants accumulating sorbitol, but this did not affect sucrose accumulation in the culm. The activity of oxidative reactions in the pentose phosphate pathway and the non-reversible glyceraldehyde-3-phosphate dehydrogenase reaction were elevated to replenish the reducing power consumed by sorbitol synthesis. Sorbitol-producing sugarcane generated 30%-40% less aerial biomass and was 10%-30% shorter than control lines. Leaves developed necrosis in a pattern characteristic of early senescence, and the severity was related to the relative quantity of sorbitol accumulated. When the Zymomonas mobilis glucokinase (zmglk) gene was co-expressed with mds6pdh to increase the production of glucose-6-phosphate, the plants were again smaller, indicating that glucose-6-phosphate deficiency was not responsible for the reduced growth. In summary, sorbitol hyperaccumulation affected sugarcane growth and metabolism, but the outcome was not lethal for the plant. This work also demonstrated that impressive yields of alternative products can be generated from the intermediates of sucrose metabolism in Saccharum spp.

In vitro Induction of Colchiploidy in an Intergeneric Hybrid of Sorghum*Saccharum

A rare hybrid of Sorghum×Sugarcane was produced at Sugarcane Breeding Institute during 1996 which had a chromosome number 2n=66. This hybrid lacked vigor and was poor with respect to agronomic traits. Attempts were made to create genetic variation in this hybrid through tissue culture and colchicine treatment. Calli induction and their differentiation to plantlets were obtained on modified MS medium. Different concentrations of colchicine (25 mg/l, 50 mg/l, 75 mg/l and 100 mg/l) were added to the differentiation medium. There was no differentiation in the medium containing 75 mg/l and 100 mg/l colchicine, while calli treated with 25 mg/l and 50 mg/l colchicine produced 230 plants. The regenerated plants obtained were rooted, hardened and established in pots as well as in the field and cytomorphologically characterized. Though the somaclones were morphologically similar to the original hybrid in almost all the characters, the cytological analysis revealed the occurrence of polyploidy in these calli clones. Chimeric plants were also obtained during in vitro polyploidization. The results indicate that colchicine could be efficiently utilized for induction of polyploidy in Saccharum hybrids.

Arabidopsis Sucrose Transporter AtSUC9. High-Affinity Transport Activity, Intragenic Control of Expression, and Early Flowering Mutant Phenotype

AtSUC9 (At5g06170), a sucrose (Suc) transporter from Arabidopsis (Arabidopsis thaliana) L. Heynh., was expressed in Xenopus (Xenopus laevis) oocytes, and transport activity was analyzed. Compared to all other Suc transporters, AtSUC9 had an ultrahigh affinity for Suc (K(0.5) = 0.066 +/- 0.025 mm). AtSUC9 showed low substrate specificity, similar to AtSUC2 (At1g22710), and transported a wide range of glucosides, including helicin, salicin, arbutin, maltose, fraxin, esculin, turanose, and alpha-methyl-d-glucose. The ability of AtSUC9 to transport 10 glucosides was compared directly with that of AtSUC2, HvSUT1 (from barley [Hordeum vulgare]), and ShSUT1 (from sugarcane [Saccharum hybrid]), and results indicate that type I and type II Suc transporters have different substrate specificities. AtSUC9 protein was localized to the plasma membrane by transient expression in onion (Allium cepa) epidermis. Using a whole-gene translational fusion to beta-glucuronidase, AtSUC9 expression was found in sink tissues throughout the shoots and in flowers. AtSUC9 expression in Arabidopsis was dependent on intragenic sequence, and this was found to also be true for AtSUC1 (At1g71880) but not AtSUC2. Plants containing mutations in Suc transporter gene AtSUC9 were found to have an early flowering phenotype under short-day conditions. The transport properties of AtSUC9 indicate that it is uniquely suited to provide cellular uptake of Suc at very low extracellular Suc concentrations. The mutant phenotype of atsuc9 alleles indicates that AtSUC9 activity leads to a delay in floral transition.

Allelopathic, Autotoxic, and Hormetic Effects of Postharvest Sugarcane Residue

With green sugarcane (interspecific hybrids of Saccharum spp.) harvesting, 6 to 24 Mg ha−1 of postharvest residue is deposited on the field surface covering the sugarcane stubble that must reemerge for several ratoon crops. The objectives of this research were to: (i) determine if postharvest residue possesses allelopathic, autotoxic, and hormetic properties; (ii) determine the interaction of soil type with possible autotoxic effects; and (iii) identify a reliable indicator species. Extract concentrations consisted of 0, 0.1, 10, 25, and 100% of the original solution of a 1:28 tissue to water extract. The higher concentrations of residue extracts exhibited autotoxicity by delaying early leaf development. The lower extract concentration of 10% increased sugarcane bud germination by 45% compared with the control, indicating hormetic effects. Allelopathic activity on tall morninglory (Ipomoea hederacea Jacq.) was more pronounced on a light soil; germination and radical length were reduced by all concentrations by an average of 42% and 8 mm, respectively, compared with the control. Seedling dry weights were reduced by an average of 10 mg by the 10, 25, and 100% extract concentrations relative to the control. On the heavy soil, only the 100% concentration reduced radical length and weight by 5 mm and 4 mg, respectively, relative to the control. Extract effects on oat (Avena nuda L.), rye (Secale cereale L.), and tomato (Lycopersicon esculentum Mill.) showed poor correlation with effects on sugarcane. Chemical analysis by gas chromatography/mass spectrotometry indicated the extract contained benzoic acid. Further studies are needed to establish the impact of benzoic acid in natural settings.

Microsatellite DNA marker-assisted selection ofSaccharum spontaneum cytoplasm-derived germplasm

New lines of Saccharum hybrids with an array of S. spontaneum cytoplasm backgrounds are reported. To expand the genetic base of sugarcane, we made eleven bi-parental crosses between ten S. spontaneum (S) and six commercial-type sugarcane (C) clones during the 2001 crossing season. Prior to crossing, all the maternal S. spontaneum inflorescences were emasculated by immersion in a 50°C circulating water bath for 5 minutes. Analysis of microsatellite fingerprints between parents and progeny allowed us to classify 1,952 progeny grown out from these crosses into four genotypic classes. Class H progeny inherited microsatellite alleles from both the S. spontaneum and the commercial-type parents and were, therefore, considered being F1 hybrids. Class S and Class C progeny inherited microsatellite alleles only from one parent and were considered to be either selfs of either parent or F1 hybrids that only inherited allele(s) from one parent. Class X progeny inherited non-parental microsatellite allele(s) in addition to the allele(s) from the maternal S. spontaneum parent and were considered to be contaminants. With the exception of one cross, eight to ten Class H progeny were pre-selected from each cross while still in seedling greenhouse and were backcrossed with commercial-type sugarcane clones. The remaining progeny were transplanted into a breeding nursery for phenotypic evaluation that concurred with the molecular classification. Pearson Correlation Coefficients between molecular and phenotypic classifications were inconsistent that justified the need of molecular markers in the selection process. This study demonstrated that the molecular approach of fingerprinting progeny to confirm parentage prior to field planting even with only one microsatellite marker might substantially increase selection efficiency.

Characterization of Intergeneric Hybrids of Saccharum using Molecular Markers

The potential use of RAPD markers in identifying genuine intergeneric hybrids of Saccharum was examined in 12 hybrids of Saccharum with Erianthus spp., Sorghum bicolor and Zea mays. In the three groups of hybrids examined, RAPD markers could precisely identify the true hybrids of Saccharum officinarum × Sorghum bicolor and Saccharum officinarum × Zea mays. Though Erianthus had a very distinct RAPD profile and as many as 107 Erianthus-specific bands were identified, a decisive profile that can identify all the hybrids could not be obtained. The strong molecular differentiation between S.officinarum and Erianthus was not adequately resolved in the RAPD profiles of their hybrid progenies which suggest that more refined molecular techniques will be required for the characterization of Saccharum–Erianthus hybrids.

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.

Sugarcane Leaf Nutrient Concentrations: With or Without Midrib Tissue

The literature on sugarcane (interspecific hybrids of Saccharum spp.) leaf-nutrient composition usually reports values either with (W) or without (WO) the midrib tissue, but not for both. The removal of the midrib adds an extra step to the sampling process. The effects of sampling time (May and October) and method (W and WO midrib) on leaf-blade nutrient concentration of cultivar CP 78-1628 were investigated on a Margate sand (siliceous, hyperthermic Mollic Psammaquents) in a split-plot randomized complete block design. The presence of the midrib resulted in decreased concentrations of nitrogen (N) phosphorus (P), calcium (Ca), magnesium (Mg), zinc (Zn), manganese (Mn), and iron (Fe) in the leaf sample to varying degrees, but increased concentration of potassium (K). Simple correlation coefficients between samples analyzed W and WO the midrib were ≥0.75 for P, Ca, Mg, and Mn in May. The percent-errors of predicting WO midrib values from W midrib values were greater than 20 when tested with published data. Although differences between W and WO midrib were verified for sugarcane leaf-nutrient compositions, at this time it is not possible to predict WO nutrient concentration from W data. When reporting sugarcane leaf-nutrient values, therefore, a statement on the sampling method with regard to the midrib must be included. Estimated differences between sugarcane leaf-nutrient concentrations W and WO midrib values were ≥10.0, ≥1.0, and ≤1.2 g kg− 1 for N, P, and K, respectively, when W midrib leaf-nutrient concentrations were lower than the published critical W midrib value. This result shows that it will be important for sugarcane growers and researchers to use the appropriate critical value (WO or W midrib) for N and P, but not for K.

Sugarcane Yield, Sugarcane Quality, and Soil Variability in Louisiana

This study was conducted to determine the extent of temporal and spatial variability present in commercially cultivated sugarcane (interspecific hybrids ofSaccharumspp. cv. LCP 85‐384) grown in South Louisiana. Sugarcane fields at two locations were harvested for three consecutive years (2001–2003) in a grid pattern with a single‐row, chopper harvester and a field transport wagon equipped with electronic load sensors to determine cane yields. Sugar yield and quality were determined from a random cane sample from each grid cell, and soil samples were collected after harvest from each grid cell (2002–2004). At each location, the majority of soil properties exhibited nonnormal distributions with coefficients of variation ranging from 1 to 56% over all years and locations, and all soil properties were spatially correlated with the range varying from 26 to 241 m. Cane and sugar yields and sugar quality parameters at both locations were found to exhibit nonnormal distributions in selected years, and the coefficients of variation ranged from 5 to 20% over all years and locations. Cane and sugar yields and quality parameters were spatially correlated with a range varying from 26 to 187 m with the exception of theoretically recoverable sugar and fiber at one location in 2003. Soil S and Ca/Mg ratio were correlated to all sugar parameters at one location, and soil organic matter and soil buffer pH were correlated to all sugar parameters at the second location. These data would indicate that sufficient variability exists in commercially produced Louisiana sugarcane to justify a precision agricultural management approach.

Induction of Flowering in a Sorghum*Saccharum Hybrid through Gamma Irradiation of Calli.

The calli of a Sorghum bicolor×Saccharum officinarum hybrid was irradiated at different doses of gamma radiation to induce normal flowering and panicle emergence in this hybrid. Fifty one somaclones were regenerated from the irradiated calli and field planted during May, 2004. One of the somaclones (SSS-03/152) flowered during November, 2004 producing an inflorescence, similar to that of sugarcane. This somaclone was found to be pollen sterile, but had apparently normal female reproductive structures.