Blackberries, collectively known as Rubus L. subgenus Rubus Watson, are a group of taxonomically complex plants grown for their succulent aggregate fruits. Blackberry production in the United States has risen dramatically within the last decade, in part because of their healthful phytochemical content (Cho et al., 2004; Siriwoharn et al., 2004). They are an increasingly popular component of small farms across the United States because they are of high value and can be sold successfully using a variety of marketing strategies. However, a major challenge to increasing traditional, Midwest blackberry production is the plant's lack of winterhardiness. Winter temperatures below −18 °C reduce yield; as low temperatures approach −28 °C, flower buds for the following season's crop are virtually destroyed (Funt et al., 2000; R.C. Funt, unpublished data). Because canes can be managed as annuals, the two recently released primocane-fruiting (PF) cultivars from the University of Arkansas’ fruit breeding program, Prime-Jan and Prime-Jim (Clark et al., 2005), might help producers minimize annual yield fluctuations and improve the commercial potential of blackberry in U.S. Department of Agriculture climate zones 6 and lower.
To determine if PF blackberries offer economic and production advantages, trial plantings of Prime-Jan and Prime-Jim have been established in several production regions. Although these cultivars have the potential to be widely adapted and to fruit over an extended period (Clark et al., 2005), current evidence suggests that their yield potential may not be realized in areas with early fall frosts or extreme midsummer temperatures (Stanton, 2005). For instance, early frosts significantly shortened the first fall harvest season of Prime-Jan and Prime-Jim planted in trial at Geneva, N.Y. (C.A. Weber, personal communication). In Arkansas, Prime-Jan and Prime-Jim flowered and fruited when average daily high temperatures were typically 30–35 °C. In these trials, a reduction in or damage to flowering and fruiting was observed when daytime highs were 29.4 °C or higher for 5 to 8 d in a row (Clark et al., 2005; J.R. Clark, unpublished data). In contrast, fruit yields were substantially higher in Oregon, where average daily high temperatures during flowering were 28 °C or less.
Little information has been published concerning the effects of temperature on blackberry floral competence. In our preliminary observations, growth chamber grown PF blackberries flowered and fruited normally under a regimen of 23.9/12.8 °C day/night temperatures (LT). Primocanes grown at 29.4/18.3 °C (MT) were shorter, more numerous, and had more nodes and laterals per cane. In addition, primocanes of plants grown at MT had fewer flowering nodes and set ≈20% fewer fruits than those of their LT counterparts. Primocanes grown at 35.0/23.9 °C (HT) produced almost ten times the laterals per plant, more nodes per plant, and more nodes per cane but exhibited a lower percent of flowering nodes and did not set fruit. Flowers of this latter group were visually distinct: flower diameter was smaller, filaments and styles were shorter, and some flowers had noticeably fewer anthers (Stanton, 2005).
Here we report subsequent research quantifying the effects of increased temperature on male and female floral competence in growth chamber grown Prime-Jan and Prime-Jim PF blackberry plants. We assessed male floral competence by gauging the relative viability and germinability of pollen collected from flowers cultivated at the three temperature regimens designated above and by calculating the effective lifespan or longevity (germinability over time) of dehisced pollen held at 23.9 and 35.0 °C. We evaluated female floral competence as affected by temperature by comparing duration of stigmatic receptivity in LT-, MT-, and HT-grown flowers. We measured the pistil density per receptacle and the drupelet set within receptacles of hand-pollinated flowers. LT- and HT-developed floral buds were also examined by light microscopy for morphological abnormalities.
Brewbaker, J.L. & Kwack, B.H. 1964 The calcium ion and substances influencing pollen growth 145 151 Linskens H.F. Pollen physiology and fertilization Elsevier Amsterdam
Cho, M.J., Howard, L.R., Prior, R.E. & Clark, J.R. 2004 Flavonoid glycosides and antioxidant capacity of various blackberry, blueberry and red grape genotypes determined by high-performance liquid chromatography/mass spectrometry J. Sci. Food Agr. 84 1771 1782
Clark, J.R., Moore, J.N., Lopez-Medina, J., Finn, C. & Perkins-Veazie, P. 2005 ‘Prime-Jan’ (‘APF-8’) and ‘Prime-Jim’ (‘APF-12’) primocane-fruiting blackberries HortScience 40 852 855
Eisa, H.M. & Wallace, D.H. 1969 Factors influencing petaloidy expression in the carrot, Daucus carota L J. Amer. Soc. Hort. Sci. 94 647 649
Funt, R.C., Ellis, M.A., Williams, R., Doohan, D., Scheerens, J.C. & Welty, C. 2000 Brambles—production, management and marketing Ohio Coop. Ext. Bul. 782
Galen, C. & Plowright, R.C. 1987 Testing the accuracy of using peroxidase activity to indicate stigma receptivity Can. J. Bot. 65 107 111
Hedhly, A., Hormaza, J.L. & Herrero, M. 2003 Effect of temperature on stigmatic receptivity in sweet cherry, Prunus avium L Plant Cell Environ. 26 1673 1680
Hedhly, A., Hormaza, J.L. & Herrero, M. 2005 The effect of temperature on pollen germination, pollen tube growth and stigma receptivity in peach Plant Biol. 7 476 483
Hernandez, L.D. & Vierling, E. 1993 Expression of low molecular weight heat-shock proteins under field conditions Plant Physiol. 101 1209 1216
Kim, S.Y., Hong, C.B. & Lee, I. 2001 Heat shock stress causes stage-specific male sterility in Arabidopsis thaliana J. Plant Res. 114 301 307
Lohar, D.P. & Peat, W.E. 1998 Floral characteristics of heat-tolerant and heat-sensitive tomato (Lycopersicon esculentum Mill.) cultivars at high temperature Scientia Hort. 73 53 60
Lozano, R., Angosto, T., Gomez, P., Payan, C., Capel, J., Huijser, P., Salinas, J. & Martinez-Zapater, J.M. 1998 Tomato flower abnormalities induced by low temperatures are associated with changes of expression of MADS-box genes Plant Physiol. 117 91 100
Miller, A.R., Dalmasso, J.P. & Kretchman, D.W. 1987 Mechanical stress, storage time and temperature influence cell wall-degrading enzymes, firmness and ethylene production by cucumbers J. Amer. Soc. Hort. Sci. 112 666 671
Peet, M.M., Willits, D.H. & Gardner, R. 1997 Response of ovule development and post-pollen production processes in male-sterile tomatoes to chronic, sub-acute high temperature stress J. Expt. Bot. 48 306 101 111
Peet, M., Sato, S., Clemente, C. & Pressman, E. 2003 Heat stress increases sensitivity of pollen, fruit and seed production in tomatoes (Lycopersicon esculentum Mill.) to non-optimal vapor pressure deficits Acta Hort. 618 209 215
Saini, H.S., Sedgely, M. & Aspinall, D. 1984 Developmental anatomy in wheat of male sterility induced by heat stress, water deficit or abscisic acid. Aust. J Plant Physiol. 11 243 253
Sanmiya, K., Suzuki, K., Tagiri, A., Egawa, Y. & Shono, M. 2005 Ovule-specific expression of the genes for mitochondrial and endoplasmic reticulum localized small heat-shock proteins in tomato flower Plant Cell Tissue Organ Cult. 83 245 250
Sanzol, J., Rallo, P. & Herrero, H. 2003a Asynchronous development of stigmatic receptivity in the pear (Pyrus communis; Rosaceae) flower Amer. J. Bot. 90 78 84
Sanzol, J., Rallo, P. & Herrero, M. 2003b Stigmatic receptivity limits the effective pollination period in ‘Agua de Aranjuez’ pear J. Amer. Soc. Hort. Sci. 128 458 462
Sato, S., Peet, M.M. & Gardner, R.G. 2004 Altered flower retention and developmental patterns in nine tomato cultivars under elevated temperature Scientia Hort. 101 95 101
Siriwoharn, R., Wrolstad, R.E., Finn, C.E. & Pereira, C.B. 2004 Influence of cultivar, maturity and sampling on blackberry (Rubus L. hybrids) anthocyanins, polyphenolics and antioxidant properties J. Agr. Food Chem. 52 8021 8030
Stafne, E.T., Clark, J.R. & Rom, C.R. 2001 Leaf gas exchange response of ‘Arapaho’ blackberry and six red raspberry cultivars to moderate and high temperatures HortScience 36 880 883
Stanton, M.A. 2005 The effects of heat on flowering and fruiting of two primocane-fruiting cultivars of blackberry, Rubus spp., Prime Jan™ and Prime Jim™ The Ohio State Univ Columbus, Ohio MS Thesis.
Summerfield, R.J., Roberts, E.H., Ellis, R.H. & Lawn, R.J. 1991 Towards the reliable prediction of time to flowering in six annual crops. I. the development of simple models for fluctuating field environments Expt. Agr. 27 11 31
Tsukaya, H., Takahashi, T., Naito, S. & Komeda, Y. 1993 Floral organ-specific and constitutive expression of an Arabidopsis thaliana heat-shock HSP18.2::GUS fusion gene is retained even after homeotic conversion of flowers by mutation Mol. Gen. Genet. 237 26 32
Turemis, N. & Derin, K. 2000 Determination of the viability and production of pollen and suitable pollen germination medium in some blackberry (Rubus fruticosus L.) cultivars. Turkish J Agr. For. 24 637 642
Vara Prasad, P.V., Craufurd, P.Q. & Summerfield, R.J. 1999 Fruit number in relation to pollen production and viability in groundnut exposed to short episodes of heat stress Ann. Bot. (Lond.) 84 381 386
Wolyn, D.J. & Chahal, A. 1998 Nuclear and cytoplasmic interactions for petaloid male-sterile accessions of wild carrot (Daucus carota L.) J. Amer. Soc. Hort. Sci. 123 849 853
Young, L.W., Wilen, R.W. & Bonham Smith, P.C. 2004 High temperature stress of Brassica napus during flowering reduces micro- and megagametophyte fertility, induces fruit abortion, and disrupts seed production J. Expt. Bot. 55 396 485 495