Originally published as:
Craddock, J.H. and Bassi, G.  (1999)  Effect of clonally propagated interspecific hybrid chestnut rootstocks on short-term
graft incompatibility with four cultivars of Italian "Marrone".  In: Salesses, G. (ed.) Proc. 2nd International Chestnut
Symposium, Bordeaux, France.  Acta Horticulturae 494: 207-121

J. Hill Craddock
University of Tennessee at Chattanooga
Dept. of Biological and Environmental Sciences
615 McCallie Avenue
Chattanooga, TN 37403 2598
USA

Guido Bassi
Bassi Vivai,
Via Tonello 17,
12100 Cuneo, Italy
 

Keywords: Castanea sativa , propagation

Abstract

        Differences between clonally-propagated interspecific hybrid chestnut rootstocks were observed when short-term graft compatibility with four Italian cultivars of 'Marrone' was investigated. The rootstock clone CA07 had the highest overall percentage of successful grafts. It had an "excellent" compatibility rating with two of the 'Marrone' cultivars but "good" or "poor" ratings with the other two. CA15 had a lower percentage of graft success than CA07 but the unions formed were rated as "good" for all four 'Marrone.' The success rate for CA74 was worse than that for CA07 and CA15 and its compatibility ratings ranged from "good" to "poor." As rootstocks for 'Marrone,' the clones CA90 and CA118 were almost total failures.
 

Introduction

        Availability of graft-compatible Phytophthora -resistant chestnut rootstocks is limiting the growing of chestnut in many parts of Italy where ink disease (caused by Phytophthora cambivora and P. cinnamomi ) is damaging or destroying traditional groves of the European Castanea sativa cultivars. Genetic resistance to Phytophthora occurs in the Asian chestnut species C. crenata and C. mollissima (Rutter et al, 1992). However, graft incompatibility between species (Huang et al. 1994; Santamour, 1988) has largely prevented the use of the resistant species as rootstocks for the European varieties. In the present study, the effect of clonally-propagated interspecific hybrid rootstocks on short-term graft compatibility with four Italian 'Marrone' cultivars was investigated under nursery field conditions in Cuneo Province, northwestern Italy. The clonal rootstocks used in the study were Phytophthora -resistant Euro-Japanese hybrids released by the Institute National de la Recherche Agronomique, Bordeaux, France (INRA-Bordeaux). These hybrids have been extensively tested as "rootstock candidates" for French chestnut cultivars (Chapa et al. , 1990). The results of grafting experiments have been variable and "generally mediocre" (Breisch, 1992a) although several promising rootstock-scion combinations were identified (Breisch, 1992b). In addition to genetic incompatibility with clones of Castanea sativa , mechanical difficulty (poor quality of the layered shoots), agronomic factors (bad weather) and phytosanitary problems such as chestnut mosaic virus (ChMV), have limited the wider deployment of the Phytophthora resistant clonal rootstocks. However, based on their own merits, several of the hybrids were named and released as nut-bearing varieties (Breisch, 1993; Chapa, 1987). Although widely available for many years to growers in northwestern Italy, the French Euro-Japanese hybrids have been evaluated only for their nut-bearing qualities and never as rootstocks for Italian chestnut cultivars. The objective of the present study was to test the best available Phytophthora -resistant clones as rootstocks for four of the most important Italian 'Marrone' cultivars. The current paper reports on one year of observations of short-term graft compatibility in the nursery.
 

Materials and Methods

        The clonally-propagated rootstocks used in the study were the Phytophthora -resistant Euro-Japanese hybrids 'Marsol' (CA07), 'Maraval' (CA74), 'Ferosacre' (CA90), 'Marigoule' (CA15) and 'Marlhac' (CA118) grown from in vitro meristem culture. Characteristics of the rootstocks are listed in Table 1. The grafted cultivars were 'Marrone di Chiusa Pesio,' 'Marrone di Marradi,' 'Marrone di Castel del Rio' and 'Marrone di San Mauro Saline.' The marroni are described in Table 2. Twenty-five of each rootstock per cultivar were budded in September 1997 and all unsuccessful buds were replaced with a whip and tongue graft in the following spring as is normal nursery practice in the Cuneo area (Craddock and Bassi, 1993). A severe late frost occurred on 25 May 1998 that damaged or killed many of the grafted plants. Because little dormant scionwood was still available at that late date, few of the surviving rootstocks were re-grafted. Several additional cultivars used after the 25 May killing frost are described in Table 3. The controls included scions of the four 'Marrone' grafted onto open pollinated seedlings of the same four cultivars (each cultivar grafted onto its own seedlings) or onto "wild type" Castanea sativa seedlings as per the customary nursery practice in the Cuneo area (Craddock and Bassi, 1993).
        Evidence of short-term graft compatibility was evaluated (Table 4) by calculating the percentage of successful grafts for each scion/rootstock combination and assigning each group to one of four levels of graft compatibility based on a qualitative assessment of the graft union as follows: excellent = perfect union; good = graft union well formed but with callus tissue visible; fair = union imperfectly formed with callus visible and bark peeling; poor = deformed or swollen graft union and/or different diameters between rootstock and scion. The number of rootstocks with chestnut blight cankers, caused by the fungus Cryphonectria parasitica , was recorded for all treatments and controls.
 

Results

        Significant differences between rootstocks were observed. A summary of results is presented in Table 5. CA07 had the highest percentage of successful grafts, overall. It seems particularly well suited for the 'Marrone di San Mauro Saline' (88% take, "excellent" compatibility rating). Although CA07 had an "excellent" compatibility rating with two of the 'Marrone' cultivars, it had only "good" and "poor" ratings in combination with the other two. CA15 had a slightly lower percentage of graft success than CA07 but the unions formed were rated as "good" for all four "Marrone." The success rate for CA74 was worse than that for CA07 and CA15 and the compatibility ratings ranged from "good" for two of the 'Marrone' to "fair" and "poor" for the other two cultivars.
        The clones CA90 and CA118 were almost total failures in terms of percentage of successful grafts, although the few grafts on CA118 that did survive were rated as having "good" graft unions for 'Marradi' and 'Chiusa Pesio.' Leafing-out occurred very early for all of the cultivars grafted onto these two rootstocks. A killing frost on 25 May 1998, eliminated almost all of the grafted trees on CA118 and effectively destroyed every plant on CA90. Many of the rootstocks re-sprouted after the freeze, but the scions were dead. Table 5 also includes data from grafts that were made onto CA90 after the 25 May frost. In this case, graft success was 53% for 'Marrone di Chiusa Pesio' and 63% for 'Castagna della Madonna,' but the quality of the unions was apparently very good.
        Results of the control grafts onto open pollinated seedlings of the interspecific hybrid cultivar 'Marigoule' (CA15) were generally rated as "poor" quality and had percent takes slightly lower than that for grafts onto the clonal rootstocks (approx. 50% take). In comparison, grafts onto seedling of the 'Marrone' cultivars and wild-type seedlings, yielded "excellent" ratings and relatively high percentages of successful grafts.
        'Marrone di Marradi' was successfully grafted onto four of the five rootstocks, with CA07 giving the highest percentage of takes (72%), CA118 giving the lowest (7%) and CA15 and CA74 at intermediate levels (42% and 56%, respectively). All of the successful graft combinations with 'Marradi' were rated as "good." There were no successful grafts of 'Marradi' on CA90.
        'Marrone di Castel del Rio' was unusual because, even though the percentage of successful takes on CA07 was high (75%), the quality of the graft union was rated as "poor." For this cultivar, only CA15 yielded grafts rated "good" albeit at a very low success rate (23%). None of the rootstocks were rated as 'excellent' for 'Castel del Rio.' Grafts onto the hybrid seedling controls gave poor results.
        'Marrone di Chiusa Pesio' had its highest percent take when grafted onto CA15 (79%), but the overall quality of the graft unions was better when it was grafted onto CA07, although the success rate was much lower (31%).
        'Marrone di San Mauro Saline' gave very good results on both CA07 (88% take) and CA15 (84% take), but the quality of the union was better on 'CA07.' 'CA74 was a mediocre rootstock and there were no successful grafts of 'San Mauro' on CA90 or 'CA118.' Grafts on the hybrid seedling controls gave poor results.
 

Discussion

        Ink disease, caused by Phytophthora spp. may be one of the most limiting factors to chestnut-growing in Italy, today. The impact of the disease has been particularly severe in the traditional 'Marrone' orchards of Cuneo province, where historically these valuable chestnut cultivars were grown on rich alluvial soils near the valley floors. Ink disease has nearly eliminated the cultivar 'Marrone di Chiusa Pesio' from its native area. There is an urgent need to propagate this variety onto Phytophthora -resistant rootstocks to ensure its survival as a commercial cultivar.
According to Breisch (1992a,b), the appearance of the graft union in the nursery is a good predictor of the tree's subsequent orchard performance. Good compatibility is indicated by a well healed union, without swelling, of uniform diameter. Open pollinated seedlings of the Phytophthora -resistant hybrid cultivars 'Marsol' (CA07) and 'Marigoule' (CA15) may be suitable for the propagation of many Euro-Japanese hybrid cultivars. These two cultivars are now widely grown in northern Italy and many plants grafted onto their seedlings are commercially available. However, CA15 seedlings are not suitable as rootstocks for the C. sativa cultivars examined in this trial because of lower rates of graft success ( from 30 to 50 percent take) and poor compatibility ratings. And seedlings will be highly variable in their resistance to Phytophthora spp . and Cryphonectria parasitica .
        As a clonal rootstock, CA07 is very promising and worthy of further trial in the Cuneo area. It gave excellent results when used as a rootstock for all of the cultivars used in this experiment, particularly in combination with 'Marrone di San Mauro Saline.' And, even though the percent take with 'Marrone di Chiusa Pesio' on CA07 was not very high, the quality of the graft union appeared near perfect. The rootstock CA15 is also deserving of further study. The grafted plants from this study will be planted in an orchard setting for future observations on long-term compatibility, vigor, and yield. CA74 gave mediocre results with a low percentage of successful grafts. It would not be recommended for any of the four marroni cultivars tested here. The apparent lack of graft compatibility for the rootstocks CA90 and CA118 may be due to problems of cold hardiness, especially the late spring frost suffered by the plants shortly after the grafts had been executed. Another trial using CA90 and CA118 as rootstocks for 'Marrone di Chiusa Pesio' and two other C. sativa cultivars was very successful when the grafting date was delayed until 25 May. Even though grafting could be delayed (effectively lengthening the grafting season in Cuneo), induced lack of cold hardiness may be a persistent problem as the grafted plants mature. Higher frost sensitivity in older, orchard-grown trees grafted on CA90 has been observed for the French cultivar 'Marron d'Olargues' (Breisch, 1992a).
 

References

Breisch, H. (1992a) Des porte-greffe resistants à la maladie de l'encre. Infos-Ctifl 87: 39-42.

Breisch, H. (1992b) Compatibility tests between the main French varieties of chestnut trees and ink-resistant hybrid rootstocks. Pages 41-53 in: Wallace, R.D. and Spinella, L. G. (eds.). Proc. World Chestnut Industry Conf., Morgantown, WV. Chestnut Marketing Assoc., Alachua, FL, USA.

Breisch, H. (1993) Le verger de châtaignier, une culture à part entiere. L'Arboriculture Fruitiere 458: 33-38.

Chapa, J., Chazerans, P. and Coulie, J. (1990) Multiplication vegetative du chataignier. Amelioration par greffage de printemps et bouturage semi-ligneux . L'Arboriculture Fruitiere 431: 41-48.

Chapa, J. (1987) Châtaignes et Marrons, varietes inscrites au catalogue officiel (INRA Bordeaux). L'Arboriculture fruitiere 399: 21-30.

Craddock, J.H. and Bassi, G. (1993) Nursery application of whip and tongue grafting on chestnut. Pages 195-198 in: International Congress on Chestnut, Spoleto, Italy, Oct. 20-23, 1993. Comunita Montana Monti Martani e Serano, Spoleto. 687 pp.

Huang, H., Norton, J.D., Boyhan, G.E. and Abrahams, B.R. (1994) Graft compatibility among chestnut (Castanea) species. J. Amer. Soc. Hort. Sci. 119(6): 1127-1132.

Rutter, P.A., Miller, G. and Payne, J.A. (1990) Chestnuts (Castanea). Pages 761-788 in: Moore, J.N. and Ballington, J.R.Jr., (eds.) Genetic Resources of Temperate Fruit and Nut Crops. Acta Horticulturae 290. ISBN 9066052740

Santamour, F.S., Jr. (1988) Graft incompatibility related to cambial peroxidase isozymes in Chinese chestnut. J. Environ. Hort. 6(2): 33-39.
 

Table 1. Clonally propagated interspecific hybrid rootstocks tested for graft compatibility with four Italian cultivars of 'Marrone'

Clone	Name	Origin	Characteristicz
CA07	'Marsol'	C. crenata x C. sativa	high vigor
CA15	'Marigoule'	C. crenata x C. sativa	high vigor
CA74	'Maraval'	C. crenata x C. sativa	low vigor
CA90	'Ferosacre'	hybrid of C. mollissima	vigor varies
CA118	'Marlhac'	C. sativa x C. crenata F1	promising  clone

^z After Breisch, 1993
 
 

Table 2. Italian cultivars of 'Marrone' grafted onto five clonally propagated rootstocks to test for graft compatibility (T-bud Aug.-Sept. 1997; Whip-and-tongue April 1998).

Cultivar	Origin
Marrone di Marradi	Tuscany - Province of Firenze ("Marrone Fiorentino"type)
Marrone di Castel del Rio	Emilia-Romagna - Province of Bologna
Marrone di Chiusa Pesio	Piemonte- -Province of Cuneo
Marrone di San Mauro Saline	Veneto - Province of Verona

 
 

Table 3. Other cultivars of Castanea sativa grafted onto clonally propagated and seedling interspecific hybrid rootstocks to test for graft compatibility after the killing frost that occurred on 25 May 1998.

Cultivar	Origin
Castagna della Madonna	Piemonte - Province of Cuneo
Bracalla	Piemonte - Province of Cuneo
Belle Epine	Dordogne -  France
Marrone di Castel del Rio	Emilia-Romagna - Province of Bologna
Marrone di Chiusa Pesio	Piemonte - Province of Cuneo
M. di San Mauro Saline	Veneto - Province of Verona

 

Table 4.   Ratings used to measure evidence of short-term graft compatibility between Italian 'Marrone' and clonally  propagated rootstocks.

Qualitative assessment of the graft union:
Excellent = perfect union
Good = graft union well formed but with callus tissue visible
Fair = union imperfectly formed with callus visible and bark peeling
Poor = deformed or swollen union and/or different diameters between stock and scion.

Table 5. Percent graft success, quality ratings of the graft unions and incidence of chestnut blight for five clonally propagated interspecific hybrid chestnut rootstocks grafted to four Italian 'Marrone' and three European chestnut cultivars.

                                                                                                                                       Compatibility Rating

"Marrone"	Rootstock	% Success	Excellent	Good	Fair	Poor	Blight
Marradi	CA07	72		+			1
	CA15	42		+			0
	CA74	56		+			0
	CA90	0					1
	CA118	7		+			0
	seedlings of Marradi	70	+				-
Castel del Rio CA07 75 1
CA15 23 2
CA74 56 0
CA90 4 1
CA118 0 0
seedlings of CA15 45 0
sdlng of C. del Rio 70 -
Chiusa Pesio CA07 31 0
CA15 79 0
CA74 30 1
CA90 0 0
CA90* 53 0
CA118 7 0
sdlng of Chiusa Pesio 65 -
S. Mauro S. CA07 88 2
CA15 84 0
CA74 50 1
CA90 0 0
CA118 0 1
seedlings of CA15 53 0
sdlng of S. Mauro S. 75 -
C. Madonna CA07* 100 -
CA90* 63 -
Bracalla CA07* 96 -
Belle Epine seedlings of CA15 35 -

* Grafted after killing frost of 25 May 1998.

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