Samuel K. Asiedu

A plant growth promoting rhizobacterium and temperature effects on performance of 18 clones of potato

A survey of genotypic responses to beneficial bacterium (Pseudomonas sp. strain PsJN) was conductedin vitro andex vitro, under two temperature conditions, using eighteen clones of potato of different heat stress tolerance: temperate adapted cultivars Kennebec and Russet Burbank; heat tolerant DTO-2, DTO-28, DTO-33, LT-1, LT-2, LT-5, LT-6, LT-7, LT-8, LT-9, Y84-02, NDD277-2, Désirée, and Maine-47; and heat sensitive abscissic acid (ABA)-deficient mutants 11401-01 and 9120-05. Nodal explants taken from 6-week-old bacterized and non-bacterized control plantlets were culturedin vitro on a hormone-free potato nodal cutting medium, and placed at either 20/15 C or 33/25 C day/night temperature, 12h photoperiod and 250 µE m−2 s−1 mixture of fluorescent and incandescent light, for six weeks. The tuberization response was studiedex vitro after two weeks acclimation of 2-week old plantlets at 33/25C. The acclimated plantlets were transplanted to 3L plastic nursery pots containing peat-based Pro-Mix growing medium and placed in growth chambers at either 20/15 or 33/25 C day/night temperature, 12 h photoperiod, 475 μE m−2 s−1 light and ≈80% RH, for 12 weeks. Compared to the non-bacterized controls, bacterization significantly increased stem length of 12, shoot biomass of 9, and root biomass of 2 clones at 20/15C; and stem length of 14, shoot biomass of 15, and root biomass of 13 clones at 33/25C. High temperature increased length of internodes and had either no effect or slightly decreased node number. Temperature increase had the most dramatic effect on root development. An average shoot to root ratio decreased from 3.7 at 20/15 C to 1.7 at 33/25 C for non-bacterized plantlets and, respectively, from 4.3 to 1.5 for bacterized. The beneficial effect of bacterization on root biomass was the most pronounced in LT-1 and Maine-47 at 20/15 C and LT-8, Maine 47, DTO-2, Kennebec, NDD277-2 and 11401-01 at 33/25C. The temperature elevation did not significantly affect root biomass of LT-6, DTO-28 and Désirée. Temperature stress caused severe reduction in tuber number and tuber fresh weight. ABA-deficient mutants did not produce any tubers and LT-8, LT-9, Y84-027 and DTO-28 tuberized very poorly at 33/25C. DTO-33, Désirée, LT-1 and Kennebec gave the highest number of tubers per pot and Kennebec, LT-1, Désirée and LT-7 the highest yields at this temperature. There was no significant effect of bacterization on tuberization at 20/15 C but at 33/25 C bacterization significantly enhanced tuber number and weight in LT-7 and reduced tuber weight in DTO-2. Although there was no clear link between thein vitro response of particular clones to bacterization and their heat stress tolerance, improvement ofex vitro performance of heat tolerant LT-7 indicates that rhizosphere bacteria may play a role in clonal adaptation of potato to heat stress.

From laboratory to applications: Challenges and progress with in vitro dual cultures of potato and beneficial bacteria

In natural habitats, free-living micro-organisms play an important role in plant growth, development and adaptation to extreme environments [1–4]. They form close associations with plant roots and colonize internal and external tissues [2–5]. Production of axenic plantlets under tissue culture conditions devoids plants of these natural allies. Combination of the culture conditions, high humidity and high sugar in particular, and lack of microbial elicitors triggering or enhancing certain metabolic pathways, make tissue culture transplants vulnerable to pathogens and other environmental stresses [6]. It is well documented that plantlets have reduced photosynthetic capacity [7], lower wax deposits [8], poorly functioning stomata [9,10], underdeveloped root system, and very few leaf and root hairs [6,10]. There is a great possibility that reintroduction of certain micro-organisms or their combinations to tissue culture propagules, bacteria and vesicular-arbuscular mycorrhiza in particular, can be utilized in agricultural and horticultural practices for the purpose of transplants protection against diseases, improvement of establishment and overall performance ([3,4,6,7] and papers by A.C. Cassells and E. Wilhelm in this Proceedings).

Sprout development and processing quality changes in potato tubers stored under ethylene: 1. Effects of ethylene concentration

Ethylene effectively inhibits sprouting of potatoes (Solanum tuberosum L.) during storage, but it often darkens fry color. The objective of the work described here was to determine if altering the concentration of ethylene applied would reduce the darkening while retaining adequate sprout inhibition. Trials were conducted over three consecutive years (1991–1992, 1992–1993, and 1993–1994). Tubers of cv Russet Burbank (ca 150–300 g) were stored at 9 C for 25 wk in closed chambers in a refrigerated room under continuous exposure to 0.4, 4, 40, or 400 µL L−1 ethylene gas delivered with the ventilation airstream (ca 0.5 air exchanges per h, for 6 h each day). Untreated control and chlorpropham-treated (CIPC) check tubers were stored under the same conditions but without ethylene supplementation. Sprout number, length, and biomass, fry color, loss of tuber mass, disease, and dry matter content were evaluated at 5-wk intervals. Dose-dependent effects (400>40>4>0.4 µL L−1) of ethylene on sprout growth and fry color were observed. The 400, 40, and 4 µL L−1 ethylene treatments inhibited sprout growth as effectively as CIPC, whereas in 0.4 µL L−1 ethylene sprouting was midway between CIPC and the untreated control. Sprout mass and maximum sprout length in all ethylene treatments were significantly lower (P<0.05) than in the untreated control. Compared with the initial value (57.3 Agtron reflectance units [ARu]), after 5 wk of storage fry color was up to 5 ARu darker in the ethylene treatments, but recovered steadily at the subsequent evaluation dates. At 25 wk of storage the fry color of tubers from the 40 and 4 µL L−1 ethylene treatments were, however, still darker than tubers stored with CIPC. Inhibition of sprout growth was slightly more effective in the 400 and 40 µL L−1 ethylene treatments than in 4 µL L−1, although there were no significant differences (P<0.01) in fry color between these treatments. In comparison with the other ethylene treatments, fry color in 0.4 µL L−1 ethylene was lighter, but inhibition of sprout growth was significantly (P<0.05) poorer. There were no differences in tuber disease incidence or dry matter content between the treatments. At 25 wk, the untreated tubers had ca 50% greater loss of tuber mass than any other treatment, attributable to their heavy sprouting. Loss of tuber mass in the ethylene treatments was not significantly different (P<0.001) from that in the CIPC treatment.ResumenEl etileno inhibe eficazmente el brotamiento de la papa (Solanum tuberosum L.) durante el almacenamiento, pero a menudo oscurece el color de la fritura. El objetivo de este trabajo fue determinar si alterando la concentración de etileno aplicado se puede reducir el oscurecimiento, reteniendo una adecuada inhibición del brotamiento. Las pruebas se realizaron durante tres años consecutivos (1991–1992, 1992–1993, y 1993–1994). Tubérculos del cultivar Russet Burbank (ca.150–300 g) se almacenaron a 9EC por 25 semanas en cámaras cerradas en un cuarto refrigerado bajo continua exposición a gas etileno 0.4, 4, 40 y 400 µL L−1, repartido con la corriente de aire de ventilación (ca. 0.5 de cambios de aire, por 6 horas diarias). Los tubérculos sin tratar y los testigos tratados con cloroprofan (CIPC) fueron almacenados bajo las mismas condiciones pero sin suplemento de etileno. A cinco semanas de intervalo se evaluó el número de brotes, largo y biomasa, color de fritura, pérdida de masa del tubérculo, enfermedad y contenido de materia seca. Se observaron los efectos dependientes de la dosis de etileno (400>40>4>0.4 µL L−1) sobre el crecimiento del brote y el color de la fritura. Los tratamientos de etileno 400, 40 y 4 µL L−1 de etileno inhibieron el crecimiento del brote tanto como el CIPC y el testigo sin tratamiento, mientras que en 0.4F µL L−1 el brotamiento con etileno fue la mitad entre CIPC y el testigo sin tratamiento. La masa de los brotes y la longitud máxima en todos los tratamientos con etileno fueron significativamente menores (P<0.05) que en el testigo sin tratar. Comparado con los valores iniciales (57.3 unidades Agtron de reflectancia [ARu]), después de cinco semanas de almacenamiento, el color de fritura estuvo hasta 5 ARu más oscuro en los tratamientos de etileno, pero se recuperó regularmente en las siguientes fecha de evaluación. A las 25 semanas de almacenaje, el color de fritura de los tratamientos 40 y 4 µL L−1 de etileno, fue, sin embargo, todavía más oscuro que los tubérculos almacenados con CIPC. La inhibición de crecimiento del brote fue ligeramente más efectiva en el tratamiento con etileno 400 y 40 µL L−1 que en 4 µL L−1, aunque no hubo diferencias significativas (P<0.01) en el color de fritura entre estos tratamientos. En comparación con los otros tratamientos de etileno, el color de fritura en etileno 0.4 µL L−1 fue más ligero, pero la inhibición de brotamiento fue significativamente (P<0.05) menor. No hubo diferencias en la incidencia de enfermedades del tubérculo o contenido de materia seca entre los tratamientos. A las 25 semanas, los tubérculos sin tratar tuvieron 50% más pérdida de la masa del tubérculo que ningún otro tratamiento, atribuible a su intenso brotamiento. La pérdida de masa del tubérculo en los tratamientos con etileno no fue significativamente diferente (P<0.001) del tratamiento con CIPC.

Gelling agent and light effects onin vitro tuberization of potato cultivars

The effects of Gelrite and agar onin vitro tuberization of six potato cultivars, Atlantic, Chaleur, Cherokee, Desiree, Kennebec and Red Pontiac under low light intensity and in the dark were examined. The medium consisted of MS salts, vitamins, 6% sucrose, 2.5 mg/l kinetin and either 2 g/l Gelrite or 6 g/l agar. The cultures were kept either under diffused light with a 16 h photoperiod or in darkness at 22/19 C day/night temperatures for eight weeks. Tuberization was earlier and more uniform (a higher proportion of tubers ≥ 5 mm) on Gelrite than on agar solidified medium and earlier in the darkness than in the light. Light effects varied from cultivar to cultivar. The slowest to tuberize in light were Atlantic and Red Pontiac, the fastest, Chaleur and Cherokee. Chaleur, Cherokee and Kennebec produced significantly more large tubers and higher total tuber mass under low light than in darkness. Atlantic and Red Pontiac reacted in the opposite way. Desiree produced significantly more large tubers in the dark, but the differences in tuber mass between the dark and light conditions were not significant. Light also stimulated shoot and root growth in most of the cultures. No relation was observed between the relative maturities of the tested cultivars and their tuberization responsesin vitro.CompendioSe examinaron los efectos del Gelrite y del agar sobre la tuberizaciónin vitro de seis cultivares de papa, Atlantic, Chaleur, Cherokee, Desirée, Kennebec y Red Pontiac en baja intensidad de luz y en la oscuridad. El medio consistio de sales de MS, vitaminas, 6% de sucrosa, 2,5 mg/L de kinetin y 2 g/L de Gelrite o 6 g/L de agar. Los cultivos fueron mantenidos ya sea bajo luz difusa, con un fotoperiodo de 16 horas, o en la oscuridad a 22/19 C de temperaturas diurna/nocturna por ocho semanas. La tuberización fue más temprana y más uniforme (una proporción mayor de tubérculos ≥ 5 mm) sobre Gelrite que sobre agar solidificado y más temprana en la oscuridad que en la luz. Los efectos de la luz variaron de cultivar en cultivar. Los que tuberizaron más lento en la luz fueron Atlantic y Red Pontiac, los más rápidos Chaleur y Cherokee. Chaleur, Cherokee y Kennebec produjeron significativamente tubérculos más grandes y una masa total de tubérculos más alta bajo luz difusa que en la oscuridad. Atlantic y Red Pontiac reaccionaron de manera opuesta. Desirée produjo significativamente tubérculos más grandes en la oscuridad, pero las diferencias en masa de tubérculos entre las condiciones de oscuridad y luz no fueron significativas. La luz estimuló también el crecimiento de brotes y raíces en la mayoría de los cultivos. No se observó ninguna relación entre la madurez relativa de los cultivares estudiados y su respuesta de tuberizaciónin vitro.

Canopy Volume and Root Length Influence Greenshoulder and Internal Greening in Carrot

Greenshoulder (GS) and internal greening (IG) are physiological disorders in carrots that affect root appearance and profits to the producer. Experiments were conducted to examine genotypic sensitivity to GS and IG and to understand the relationship among canopy volume, root length, and GS and IG. Season and genotype affected GS and IG. Genotypes varied in GS and IG significantly and differentially. Regression analysis indicated a significant, negative, linear relationship between leaf area index and GS (R 2 = 0.80, P ≤ 0.0001) and IG (R 2 = 0.62, P ≤ 0.0001), implying that leaf canopy volume influenced the development of GS and IG. There were positive, significant, linear relationships between root length and GS (R 2 = 0.65, P ≤ 0.0001) and IG (R 2 = 0.35, P ≤ 0.0001) development. GS and IG are frequently observed in genotypes that have longer roots. GS and IG can be reduced by optimizing canopy volume.