Resistance to the Mexican rice borer (Lepidoptera: Crambidae) among Louisiana and Texas sugarcane cultivars

A 2-yr study to evaluate Louisiana and Texas sugarcane, Saccharum spp., cultivars for resistance to the Mexican rice borer, Eoreuma loftini (Dyar) was conducted in two locations in Texas, chosen for having different infestation levels. Criteria for assessment of resistance included percentage of bored internodes and adult emergence holes, the latter used to determine the relative impact of each cultivar on the potential areawide buildup or reduction of adult E. loftini populations. A recently released cultivar, HoCP 85-845, seemed to lose a portion of its resistance under heavy E. loftini infestation pressure, suggesting its value only in moderate-to-low infestation conditions. Cultivar CP 70-321 was the most resistant. Results indicated that cultivar LCP 85-384 was significantly (P < 0.05) more susceptible than NCo 310, traditionally the most susceptible cultivar commercially produced in Texas. In 2001, LCP 85-384, which now represents 85% of the production area in Louisiana, had the greatest moth production per hectare (17,052 +/- 3,956) under the lower infestation pressure, significantly (P < 0.05) higher than HoCP 85-845 (3,038 +/- 2,353). In a portion of the test at the high-infestation location, high levels of sodium and magnesium salt stress (15-30-cm soil depth) were associated with higher E. loftini damage in all cultivars except HoCP 91-555 and CP 70-321.     

Frost tolerance in winter wheat cultivars: different effects of chromosome 5A and association with microsatellite alleles

Frost tolerance of ten Bulgarian winter wheat (Triticum aestivum L.) cultivars (Milena, Pobeda, Sadovo-1, Enola, Kristal, Laska, Svilena, Russalka, No301 and Lozen) and five foreign cultivars (Mironovskaya 808, Bezostaya-1, Rannaya-12, Skorospelka-35 and Chinese Spring) was studied in two experimental seasons following natural cold acclimation and in one experiment carried out in controlled acclimation conditions. Considerable intercultivar variability in plant survival was observed after freezing at ?21 °C following sufficient cold acclimation, or at ?18 °C following insufficient or controlled acclimation. In seven cultivars, the effects of chromosome 5A on frost tolerance were investigated in their F₂ hybrids with chromosome 5A monosomic lines of cultivars with high, intermediate and low frost tolerance. The effects of chromosome 5A depended on the stress severity and the genetic background of the hybrids and varied even in cultivars of similar frost tolerance and vernalization requirements. Effects of other chromosomes besides 5A on frost tolerance were assumed. The analysis of six microsatellite loci located in the interval from centromere to Vrn-1 on of chromosomes 5AL, 5BL and 5DL showed that the major loci determining frost tolerance in Bulgarian winter wheats were Fr-A2 on chromosome 5AL, and, to a lesser extent, Fr-B1 on chromosome 5BL. A strong association of the 176 bp allele at locus wmc327 tightly linked to Fr-A2 with the elevated frost tolerance of cvs. Milena, Pobeda, Sadovo-1, Mironovskaya-808 and Bezostaya-1 was revealed. Relatively weaker association between frost tolerance and the presence of the 172 bp allele at locus Xgwm639 tightly linked to Fr-B1 was also observed.     

Role of oviposition preference in an invasive crambid impacting two graminaceous host crops

Oviposition preference studies of the Mexican rice borer, Eoreuma loftini (Dyar), on sugarcane, Saccharum spp., and rice, Oryza sativa L., showed that drought stressed sugarcane was 1.8-fold more attractive based on egg masses/plant than well watered sugarcane. The E. loftini susceptible sugarcane cultivar LCP 85-384 was 1.6-fold more attractive than HoCP 85-845 based on numbers of eggs per egg mass. Egg masses were 9.2-fold more abundant and 2.3-fold larger on sugarcane than on rice. Rice, however, was preferred to sugarcane on a plant biomass basis. Oviposition on sugarcane occurred exclusively on dry leaf material, which increased under drought stress. Egg masses per plant increased on drought stressed sugarcane and were correlated with several foliar free amino acids essential for insect growth and development. The more resistant (based on injury) but more attractive (based on oviposition) rice cultivar XL8 had higher levels of several free amino acids than the susceptible cultivar Cocodrie. The association of host plant characteristics to oviposition preference is discussed. Projected oviposition patterns relative to sugarcane and rice production areas were estimated for Texas and Louisiana based on the availability of each host in different regions of each state. These results suggest that, where sugarcane and rice co-occur, the majority of eggs would be found on sugarcane early in the season, because of this crop's substantially greater biomass compared with rice. Abundance later in the season would also favor sugarcane; however, the abundance on rice would be greater than expected solely based on host availability, largely because of the greater preference per gram of rice plant dry weight.     

Environmental and Seasonal Factors Affecting the Frost-induced Stage of Cold Acclimation in Cornus stolonifera Michx

Stem tissues of red-osier dogwood (Cornus stolonifera Michx.) acclimated from −3 C to −40 or −50 C in 8 to 10 weeks under a short photoperiod (9 hours) and controlled temperature conditions. During the summer months plants did not acclimate as well as at other times. The sequence of day/night temperature regimes which induced maximum acclimation was 20/15 C for 5 to 6 weeks; 15/5 C for 2 to 3 weeks; 15/5 C plus 1 hour of frost per day for 1 week. The duration of exposure to each temperature regime influenced the rate and intensity of frost-induced acclimation. Less than 5 weeks of warm temperature preconditioning at 20/15 C reduced subsequent frost-induced acclimation. The inductive influence of frost on cold acclimation was additive over 5 days of repeated exposure, but its effects after the first exposure(s) were not immediate—requiring 1 to 4 days of 15/5 C following the frost treatments for the expression of the frost-induced acclimation to be manifest. There was a 75% increase in rRNA following 3 days of frost exposure and plants in an O₂-free atmosphere during frost exposure failed to acclimate. The results suggest that seasonal acclimation behavior was due to endogenous rhythms rather than developmental stage, and that the frost-induced phase of acclimation involves aerobic metabolic processes.     

An investigation of the frost hardiness of grapevine (Vitis vinifera) during bud break

The aim of this investigation was to assess ice nucleation and frost resistance of two varieties of grapevine (Siegrebbe and Madeleine Angevine) during bud burst under radiative freezing conditions analogous to those during Spring in the UK. During bud burst, grapevines were almost entirely resistant to freezing during frosts of less than -3°C by virtue of their ability to supercool. The risk of frost damage increased significantly as bud development progressed, and once buds had passed growth stage DS3 they became more sensitive to freezing and freezing damage was more extensive. The two varieties did not differ in frost resistance but, because of its earlier developing habit, variety Siegrebbe could be more prone to frost damage in the field. Buds were more prone to damage after freezing once bud burst had commenced and the damage could not be reversed by acclimating plants for periods of 7 to 21 days at 4°C in an 8 h photoperiod. Such acclimation appeared to predispose frozen buds to more extensive damage.     

Feeding by sugarcane aphid,Melanaphis sacchari,on sugarcane cultivars with differential susceptibility and potential mechanism of resistance

Feeding behavior of Melanaphis sacchari Zehntner (Hemiptera: Aphididae) was studied on sugarcane, Saccharum spp. (Poaceae), cultivars HoCP 91‐555 (resistant), LCP 85‐384 (moderately resistant), and L 97‐128 (susceptible) using the electrical penetration graph (EPG) technique. Constitutive concentrations of total phenolics and available carbohydrates, water potential at the whole‐leaf tissue level, and free amino acids (FAAs) in phloem sap extracts, and in honeydew produced by aphids fed on L 97‐128 and HoCP 91‐555 were determined. Cultivar did not influence time for M. sacchari to access phloem sieve elements. Total time in sieve elements was ca. two‐fold greater on L 97‐128 than on HoCP 91‐555, whereas it did not differ from LCP 85‐384 in either cultivar. The mean duration of individual events associated with phloem sap ingestion was ca. 50% shorter on both HoCP 91‐555 and LCP 85‐384 than on L 97‐128. Although cultivar effects were not detected for levels of total phenolics, available carbohydrates, and water potential, two free essential amino acids, histidine and arginine, were absent from phloem sap in HoCP 91‐555. Two free essential amino acids, leucine and isoleucine, and two free non‐essential amino acids, tyrosine and proline, were absent from honeydew of aphids fed on HoCP 91‐555. These results suggest that despite apparent biosynthesis of some FAAs, the absence of important FAAs in the phloem sap of HoCP 91‐555 and the inability of M. sacchari and its endosymbionts (e.g., Buchnera) to derive specific free essential and non‐essential amino acids from other ingested molecules, possibly along with other unidentified factors, underlie the pest's decreased phloem sap ingestion and consequently reduced growth potential on HoCP 91‐555.     

Predicting economic losses from the continued spread of the Mexican rice borer (Lepidoptera: Crambidae)

The Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), is an invasive species that originated from Mexico, and it is threatening to cause major economic losses to sugarcane, Saccharum spp., and rice, Oryza sativa L., industries in Louisiana. The insect is expected to reach sugarcane and rice production areas in Louisiana by 2008, and infest all of Louisiana sugarcane and rice industries by 2035. When all sugarcane in Louisiana becomes infested, annual yield losses of $220 million would be expected for a cultivar of comparable susceptibility to LCP 85-384 (assuming this cultivar is planted on 100% of the production area). This also assumes the use of the current practice of rainfed production and one application of insecticide, which is presently used by farmers in Louisiana. Irrigation with 30 cm of water is predicted to reduce estimated losses by 29%, whereas four applications of a biorational insecticide such as tebufenozide are expected to reduce the loss in revenue by 53%. The use of the resistant 'HoCP 85-845' would reduce the projected loss in revenue by 24%. Combining all three management tactics on sugarcane, anticipated net loss in revenue would decrease by 66%. The rice industry in Louisiana is projected to suffer from a loss in revenue of $45 million when the entire state is infested. A 77% reduction in loss in revenue is expected with one application of lambda-cyhalothrin. A quarantine on east Texas sugarcane is estimated to save the Louisiana industry between $1.1 billion and $3.2 billion (depending on management) during the time needed for the insect to fully invade the state's sugarcane and rice producing area by natural migration rather than by accidental introduction. The rapid deployment of appropriate management tactics will have a key role in reducing the anticipated economic impact of E. loftini once it becomes a pest in Louisiana sugarcane and rice.     

Temperature response of plasma membranes in tuber-bearing solanum species

Permeability coefficients (Kp) of nonelectroytes were determined at several temperatures for nonacclimated and acclimated plasma membranes of the frost sensitive Solanum tuberosum and the frost resistant Solanum commersonii. In nonacclimated membranes, Kp were equal at 25°C for the two species. Kp decreased with decreased temperature in both species; however, the decrease was much greater in the frost sensitive S. tuberosum than in frost resistant S. commersonii.

Kp increased with cold acclimation. After acclimation the temperature sensitivity of Kp or activation energy (Ea) for S. tuberosum was similar to that of S. commersonii; however, Kp for S. tuberosum were lower than those for S. commersonii at all temperatures.

The differences in Kp and activation energy indicate plasma membrane differences between the species before acclimation. After acclimation there was still a difference between the plasma membranes of the two species as well as a difference between the nonacclimated and acclimated membranes of the same species.

     

Application of Impedance Spectroscopy for Selecting Frost Hardy Varieties of English Ryegrass

The frost hardening and frost damage of 12 varieties of Englishryegrass (Lolium perenne) was studied by electrical impedancespectroscopy. For the measurement of the impedance spectrum(80 Hz to 1 MHz) a 10 mm length sample was cut from the stemabove the growing point, but the growing point was included.The impedance spectra were analysed by an asymmetric distributedcircuit model. The impedance spectra were measured at two phasesof hardiness and after freezing, i.e. (a) before hardening,(b) after hardening in controlled conditions, and (c) aftercontrolled frost exposure at -16 °C after hardening. Twomodel parameters, i.e. intra- and extracellular resistance,increased with hardening. The intracellular resistance and theskewness factor before hardening, and the ratio between thosetwo parameters before and after hardening, strongly correlatedwith hardening of different varieties of English ryegrass. Theextracellular resistance and the relaxation time decreased asa result of the frost exposure at -16 °C. Cold acclimation; electrical impedance; English ryegrass; frost hardiness; impedance spectroscopy; Lolium perenne     

Plasma Membrane Alterations in Callus Tissues of Tuber-bearing Solanum Species during Cold Acclimation

Plasma membrane alterations in two tuber-bearing potato species during a 20-day cold acclimation period were investigated. Leaf-callus tissues of the frost-resistant Solanum acaule Hawkes `Oka 3878' and the frost-susceptible, commonly grown Solanum tuberosum `Red Pontiac,' were used. The former is a species that can be hardened after subjecting to the low temperature, and the latter does not harden. Samples for the electron microscopy were prepared from callus cultures after hardening at 2 C in the dark for 0, 5, 10, 15, and 20 days. After 20 days acclimation, S. acaule increased in frost hardiness from −6 to − 9 C (killing temperature), whereas frost hardiness of S. tuberosum remained unchanged (killed at −3 C). Actually, after 15 days acclimation, a −9 C frost hardiness level in S. acaule callus cultures had been achieved.     

Genetic analysis of frost hardiness traits in tuber-bearingSolanum species

The inheritance of frost hardiness and cold acclimation potential traits was studied in three segregating populations derived from a cross betweenSolanum commersonii Dun. PI 243503 (cmm) andSolanum cardiophyllum Lindl., PI 184762 (cph), two parental genotypes with contrasting frost hardiness and cold acclimation potential. The levels of frost hardiness and cold acclimation potential were expressed as the LT₅₀, the temperature at which 50% of the cells in leaf discs were killed, as measured by the ion leakage method, following a controlled freeze test There was considerable variation in both frost hardiness and cold acclimation potential in all three segregating populations (F₁ F₁ xcmm, and F₁ xcph). Frost hardiness and cold acclimation potential were not correlated, suggesting that these two traits are under independent genetic control. The analysis of generation means indicated that the variation for both traits could be best explained by an additive-dominance model, with additive gene effects the most important Broad-sense heritability was 0.73 and 0.74 in the F₁ population, for frost hardiness and cold acclimation potential, respectively, and was 0.85 for either trait in the F₁ xcmm population, indicating that these two traits are highly inheritable. Our results suggest that it should be possible to incorporate the frost hardiness and cold acclimation traits from S.commersonii into cultivated potato species.     

Chloroplast Phospholipid Molecular Species Alterations during Low Temperature Acclimation in Dunaliella

The alterations in chloroplast phospholipid acyl chain composition and phospholipid molecular species composition of Dunaliella salina (UTEX 1644) were monitored during acclimation to low temperature. Chlorophyll fluorescence yield, an indicator of chloroplast membrane stability, was used as a physical means of following the acclimation process.

Minor alterations in phospholipid acyl chain composition were evident within 36 hours of shifting the cells from 30 to 12°C. Between 36 and 60 hours, pronounced changes in the acyl chain composition of phosphatidylglycerol (PG) were observed. Changes in the acyl chain composition of phosphatidylcholine (PC) did not occur until sometime after 60 hours.

Alterations in the phospholipid molecular species during acclimation were also examined. The pattern of change observed in PC molecular species, namely a decrease in species having one saturated chain (16:0) paired with a C₁₈ acyl chain and a concomitant increase in species having two unsaturated C₁₈ acyl chains, suggests that molecular species changes augment fatty acid compositional changes as a mean of adapting to low temperature. The molecular species of PG were found to change abruptly between 36 and 60 hours following a shift to low temperature. During this time, a dramatic alteration in the threshold temperature of thermal denaturation of the photosynthetic apparatus, as measured by chlorophyll fluorescence, also occurred. Lipid compositional changes other than those associated with PG were negligible during this time. This strongly suggests that a correlation exists between the molecular species composition of PG and the thermal stability of the photosynthetic membrane.

     

High-throughput screening of bacteriorhodopsin mutants in whole cell pastes

A high-throughput screening method has been developed which enables functional analysis of bacteriorhodpsin in whole cell pastes. Reflectance spectra, from as little as 5 ml of Halobacterium salinarum cells, show close correspondence to that obtained from the purified purple membrane (PM), containing bacteriorhodopsin (BR) as the sole protein component. We demonstrate accurate quantification of BR accumulation by ratiometric analysis of BR (A_max 568) and a membrane-bound cytochrome (A_max 410). In addition, ground-state light- and dark-adapted (LA and DA, respectively) spectral differences were determined with high accuracy and precision. Using cells expressing the BR mutant D85N, we monitored transitions between intermediate-state homologues of the reprotonation phase of the light-activated proton pumping mechanism. We demonstrate that phenotypes of three mutants (D85N/T170C, D85N/D96N, and D85N/R82Q) previously characterized for their effect on photocycle transitions are reproduced in the whole cell samples. D85N/T170C stabilizes accumulation of the N state while D85N/D96N accumulates no N state. D85N/R82Q was found to have perturbed the pK_a of M accumulation. These studies illustrate the correspondence between pH-dependent ground-state transitions accessed by D85N and the transitions accessed by the wild-type protein following photoexcitation. We demonstrate that whole cell reflectance spectroscopy can be used to efficiently characterize the large numbers of mutants generated by engineering strategies that exploit saturation mutagenesis.     

Molecular Identification and Genetic Diversity Analysis of Chinese Sugarcane (<Emphasis Type="Italic">Saccharum</Emphasis> spp. Hybrids) Varieties using SSR Markers

Sugarcane (Saccharum spp. hybrids) is an important sugar and renewable bio-energy crop with a high aneu-polyploidy and complex genome. The complex characteristics of sugarcane genome enhance the difficulty of selecting elite varieties in sugarcane breeding program. The objectives of this study were to establish the molecular identities (ID) of 91 nationally or provincially released Chinese sugarcane varieties and to evaluate the extent of genetic diversity among these varieties using SSR DNA markers and two fingerprinting systems, i.e., capillary electrophoresis (CE) and polyacrylamide gel electrophoresis (PAGE). A total of 151 SSR alleles together with 20 new alleles were detected by CE and 117 SSR alleles were detected by PAGE. Primer pairs SMC336BS, SMC31CUQ, and SMC597CS amplified more than eight alleles detectable by either CE or PAGE. Polymorphism information content (PIC) values of the SSR markers varied from 0.71-0.98 with an average of 0.90 for CE, or from 0.55-0.95 with an average of 0.84 for PAGE. UPGMA method classified the 91 varieties based on the CE data into four major groups with pair-wise similarity coefficients ranging from 58% to 95%. The genetic similarity estimates within and between the four groups varied from 0.31 to 0.87, with a mean of 0.49. Our results illustrated that the 21 SSR primer pairs in combination with CE or PAGE detection system could be a very useful working tool for molecular identification of sugarcane varieties, genetic diversity assessment, and parental selection in sugarcane breeding.     

A Novel Method for Separation of Somatic Embryos from Embryogenic Suspension Cultures by Cold Treatment

This study reports a novel method for embryo separation by cold treatment of heterogeneous suspension cultures which contain embryogenic single cells, cell clusters and embryos at various stages of development. The method was applied to embryo suspension cultures of pepper (Capsicum annuum) and sugarcane (Saccharum officinarum). In both plants, single cells lost their viability dramatically over a few days while the viability of embryos remained above 95% for 25-30 days when kept at 5 °C. The effect of duration of cold treatment on embryo germination was also tested. The optimal duration of cold treatment was found to be 10 days for sugarcane and 21 days for pepper. After the cold treatment, the germination percentages were 90% and 96% for sugarcane and pepper, respectively.     

Fluorescence induction transients indicate altered absorption cross-section during light-state transitions in the cyanobacterium Synechococcus 6301

State 1–State 2 transitions in the cyanobacterium Synechococcus 6301 were observed using a lock-in amplifier to detect the fluorescence generated by a modulated excitation beam. Millisecond fluorescence induction transients were recorded for cells in State 1 and State 2. Comparison of the transients suggests that excitation energy distribution in this cyanobacterium is regulated by changes in the absorption cross-section of Photosystem II.     

Sugarcane borer (Lepidoptera: Crambidae) management threshold assessment on four sugarcane cultivars

This research assesses the potential for using different economic injury thresholds in management of a key insect pest on susceptible and resistant commercially produced cultivars of sugarcane (Saccharum spp. hybrids). In a 2-yr sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), study involving four commercially produced sugarcane cultivars and four insecticide treatment thresholds, 'LCP 85-384' and 'HoCP 91-555' were the most susceptible based on percentage of bored internodes compared with the more resistant 'HoCP 85-845' and 'CP 70-321'. In 2001, the 10% infested stalks threshold was not as effective as the 5% early season-10% late season and 5% full season for HoCP 91-555. Based on D. saccharalis injury under natural infestation conditions, susceptible cultivars seem to require a lower infestation threshold than the more resistant cultivars to achieve adequate injury reduction. Among yield components, only the theoretical recoverable sugar per stalk was significantly increased by applying insecticides. With the resistant HoCP 85-845, differences were not detected for percentage of bored internodes among treated versus untreated management regimes. The resistant HoCP 85-845 had higher levels of fiber in our study; however, no clear pattern on resistance mechanisms was established, because the resistant cultivar CP 70-321 had comparatively low levels of fiber. The development of cultivar-specific thresholds is expected to lower the amount of insecticide used for D. saccharalis management in the sugarcane industry, reduce selection pressure, and delay the development of insecticide resistance.     

Comparative effect of water, heat and light stresses on photosynthetic reactions in Sorghum bicolor(L.) Moench

Five varieties of Sorghum bicolor (L.) Moench., differing in their drought tolerance under field conditions have been used to study the effect of individual components of drought stress, namely high light intensity stress, heat stress and water stress, on their photosynthetic performance. Chlorophyll content, chlorophyll fluorescence, ribulose-1,5-bisphosphate carboxylase (Rubisco, EC 4.1.1.39) content, phosphoenolpyruvate carboxylase (PEPcase, EC 4.1.1.31) activity and photo-synthetic oxygen evolution were used as key parameters to assess photosynthetic performance. The results indicated that photochemical efficiency of photosystem II (PSII) was severely reduced by all three stress components, whereas PEPcase activity was more specifically reduced by water stress. Degradation of Rubisco and chlorophyll loss occurred under high light and water stress conditions. Of the four drought-tolerant varieties, E 36-1 showed higher PEPcase activity, Rubisco content and photochemical efficiency of PSII, and was able to sustain a higher maximal rate of photosynthetic oxygen evolution under each stress condition as compared to the other varieties. A high stability to stress-induced damage, or acclimation of photosynthesis to the individual components of drought stress may contribute to the high yields of E 36-1 under drought conditions. In the E 36-1 variety markedly higher levels of the chloroplastic chaperonin 60 (cpn 60) were observed under all stress conditions than in the susceptible variety CSV 5.Key words: Chlorophyll fluorescence, drought stress, oxygen evolution, phosphoenopyruvate carboxylase, Sorghum.      

Xylem pressure potential and chlorophyll fluorescence as indicators of freezing survival in black locust and Western hemlock seedlings

Xylem pressure potential was determined using the Scholander pressure chamber on stems of cold hardened and non-hardened black locust (Robinia pseudoacacia L.) seedlings following freezing to various nonlethal and lethal temperatures and subsequent thawing. Correlation was found between immediate xylem pressure potential and long-term seedling survival. Chlorophyll fluorescence transients were monitored using needles of western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings following freezing to various non-lethal and lethal temperatures and subsequent thawing. Immediate and repeatable differences in fluorescence transients correlated with long-term seedling survival. Methodology is described and correlations discussed relative to using either chlorophyll fluorescence or xylem pressure potential as an immediate indicator of long-term freezing survival in woody plant seedlings.